user21257: On Windows 10 I have installed the latest versions of Arena (v3.5.1) and the Lc0  engine (v0.23.1). However I have only found one weights.pb file that it will accept. The one in the link in this Q&A. But this seems rather weak, Stockfish beats it every time and it seems to make silly mistakes, particularly in the end game.
I have downloaded and unpacked several weights files from the Lc0 Networks page but they all give errors, mostly wrong format or wrong version, even those with today's date.
Can anyone suggest

What am I doing wrong? Am I downloading from the wrong place? The wrong file?
Where I can download a strong set of weights that will work with my version?

To try and give the additional information suggested by Phonon 37 in their comment:-
The version of SF I'm using is that which comes bundled with Arena, Stockfish_9_x64. Both engines are configured to run with 12 "common max CPU cores" under the UCI tab -  Options for all UCI Engines. (I've got a Ryzen 8+8 core CPU) They are paired together in the default Engines > Tournament with 10 rounds of 5 minute games.
But the real problem isn't that SF beats Lc0 10-0, it's before they even get to play. Lc0 rejects all but one weights file when I am in (F11) Engine Management >  Details, change the -w configuration on the command line and watch it throw the error in the debug window (F4) when I click on "Start this engine right now!". If I could solve this, I could try some different weights until I find one I like.

user17100: Since you didn't specify some things, I'm just going to give instructions from scratch. Since you didn't specify which version of lc0 you downloaded, make sure that it's 23.2 (from https://github.com/LeelaChessZero/lc0/releases). If you only have a cpu you want https://github.com/LeelaChessZero/lc0/releases/download/v0.23.2/lc0-v0.23.2-windows-cpu-dnnl.zip. For cpu only, the best net is no longer LD2, although it's still pretty strong. A current list of best nets of different sizes is at https://github.com/LeelaChessZero/lc0/wiki/Best-Nets-for-Lc0. At time of writing, current best 10b net is probably 58599 (https://lczero.org/get_network?sha=2b482ff696e3a4032be1b7477567661527a9fac4166591167bf0a71183f9a669). Based on what you were reporting, I'm guessing you probably had an old version of lc0 that is incompatible with newer nets. It will likely still be a few hundred elo worse than SF without a gpu, but it should at least put up a fight.
Some other minor things to consider:

Lc0 currently has weird time management when playing without an increment. This is a known bug that really should be fixed.
Default lc0 settings are for 2 threads iirc. Setting it to the number of cores you have is better with a cpu, but worse with a gpu.
You will probably get faster advice in the future by asking in the #help channel of the lc0 discord.

I hope this helps.

21257: <p>On Windows 10 I have installed the latest versions of Arena (v3.5.1) and the Lc0  engine (v0.23.1). However I have only found one weights.pb file that it will accept. The one in the link in <a href="https://chess.stackexchange.com/questions/24754/leela-chess-zero-weight-files">this Q&amp;A</a>. But this seems rather weak, Stockfish beats it every time and it seems to make silly mistakes, particularly in the end game.</p>

<p>I have downloaded and unpacked several weights files from the <a href="http://lczero.org/networks/" rel="nofollow noreferrer">Lc0 Networks page</a> but they all give errors, mostly wrong format or wrong version, even those with today's date.</p>

<p>Can anyone suggest</p>

<ol>
<li>What am I doing wrong? Am I downloading from the wrong place? The wrong file?</li>
<li>Where I can download a strong set of weights that will work with my version?</li>
</ol>

<p>To try and give the additional information suggested by Phonon 37 in their comment:-</p>

<p>The version of SF I'm using is that which comes bundled with Arena, Stockfish_9_x64. Both engines are configured to run with 12 "common max CPU cores" under the UCI tab -  Options for all UCI Engines. (I've got a Ryzen 8+8 core CPU) They are paired together in the default Engines > Tournament with 10 rounds of 5 minute games.</p>

<p>But the real problem isn't that SF beats Lc0 10-0, it's before they even get to play. Lc0 rejects all but one weights file when I am in (F11) Engine Management >  Details, change the -w configuration on the command line and watch it throw the error in the debug window (F4) when I click on "Start this engine right now!". If I could solve this, I could try some different weights until I find one I like.</p>
 17100: <p>Since you didn't specify some things, I'm just going to give instructions from scratch. Since you didn't specify which version of lc0 you downloaded, make sure that it's 23.2 (from <a href="https://github.com/LeelaChessZero/lc0/releases" rel="noreferrer">https://github.com/LeelaChessZero/lc0/releases</a>). If you only have a cpu you want <a href="https://github.com/LeelaChessZero/lc0/releases/download/v0.23.2/lc0-v0.23.2-windows-cpu-dnnl.zip" rel="noreferrer">https://github.com/LeelaChessZero/lc0/releases/download/v0.23.2/lc0-v0.23.2-windows-cpu-dnnl.zip</a>. For cpu only, the best net is no longer LD2, although it's still pretty strong. A current list of best nets of different sizes is at <a href="https://github.com/LeelaChessZero/lc0/wiki/Best-Nets-for-Lc0" rel="noreferrer">https://github.com/LeelaChessZero/lc0/wiki/Best-Nets-for-Lc0</a>. At time of writing, current best 10b net is probably 58599 (<a href="https://lczero.org/get_network?sha=2b482ff696e3a4032be1b7477567661527a9fac4166591167bf0a71183f9a669" rel="noreferrer">https://lczero.org/get_network?sha=2b482ff696e3a4032be1b7477567661527a9fac4166591167bf0a71183f9a669</a>). Based on what you were reporting, I'm guessing you probably had an old version of lc0 that is incompatible with newer nets. It will likely still be a few hundred elo worse than SF without a gpu, but it should at least put up a fight.</p>

<p>Some other minor things to consider:</p>

<ol>
<li>Lc0 currently has weird time management when playing without an increment. This is a known bug that really should be fixed.</li>
<li>Default lc0 settings are for 2 threads iirc. Setting it to the number of cores you have is better with a cpu, but worse with a gpu.</li>
<li>You will probably get faster advice in the future by asking in the #help channel of the lc0 discord.</li>
</ol>

<p>I hope this helps.</p>
