Every time I run Lightroom I get a popup message "Lightroom needs to configure your system for the [plugin name] plug-in"

This is a Lightroom issue caused by a corruption of the preferences file and appears to affect only the Windows version of Lightroom. Open the command prompt as an administrator, go to your Lightroom directory (e.g. "C:\Program Files\Adobe\Adobe Lightroom") and run the following command:

lightroom.exe -register
Why am I getting an "Unable to communicate with the server. You are either not connected to the Internet, or the server is not responding" error?

Make sure your firewall is not preventing Lightroom from accessing the Internet. You can quickly check whether this is a firewall issue by going Help > Check for Updates from Lightroom's main menu. If you receive a "Your software is up to date" message or a message about an available update, then your firewall is configured properly. Review plug-in specific FAQ for additional reason your login attempts may be failing. An error would indicate a firewall issue, unless it's a general connectivity issue and your computer is simply unable to access the Internet, period.

I am getting get badServerResponse (12152) errors, is there a fix?
This is an OS-level error meaning your system received an invalid or malformed response. The error is usually caused by antivirus and Internet security software. If you are running such products, shut them down completely. If this solves the errors, congratulations - you have identified the culprit of the problem! Fine-tune the product's security rules to stop it messing with data traffic from your hosting site or photo lab.
I get a "bad argument to ‘ipairs’ (table expected got nil)" when trying to install an update. How to fix this?
This may happen when you are updating from a much older version of the plugin due to a conflict with the code still running in Lightroom's memory. Simply restart Lightroom and you should be good to go. Never plugin versions should not have this issue any more.
What are the recommended settings for printing?

In the File Settings, set Quality to 80-85%, choose the color space or color profile for your printing lab, make sure to leave the Limit File Size To option unchecked. In the Image Sizing section, select the “Resize to Fit” option, set the size to match your target print size, for example for 5x7" prints choose Long Edge 7 in. Set Resolution to 240 pixels per inch for paper prints or 150 pixels per inch for canvas prints (check the recommended resolution with your lab).

I also recommend taking a look at the Print Size Calculator Plugin - it is designed to help figuring out the optimal print size for your photos in just a few clicks.

What are the recommended settings for web hosting?

In the File Settings, set Quality to 70-75%, set Color Space to sRGB, make sure to leave the Limit File Size To option unchecked. In the Image Sizing section, select the “Resize to Fit” option, set the size to 1400-1600 pixels (this is sufficient for most applications). It does not matter what resolution you choose, but I recommend 96 pixels per inch just to avoid confusion.

What could be causing a "ShellExecuteEx failed Code 299 - Only part of a ReadProcessMemory or WriteProcessMemory request was completed" error?
This error may appear when the .NET framework is disabled (this is the default for Windows 8) For information about enabling the .NET framework, see http://msdn.microsoft.com/en-us/library/hh506443.aspx