title: How can I get rid of the error "'folder_name' not valid as filename in directory" in TortoiseSVN 1.8.1 when checking out?
body: <p>When trying to check out a repository, I get:
  <img src="https://i.stack.imgur.com/Iyczd.png" alt="enter image description here"></p>
  
  <p>My TortoiseSVN version is:
  <img src="https://i.stack.imgur.com/DMxEC.png" alt="enter image description here"></p>
  
  <p>I downgraded to TortoiseSVN 1.7.13:
  <img src="https://i.stack.imgur.com/6jZgb.png" alt="enter image description here"></p>
  
  <p>With TortoiseSVN 1.7.13, the check out works fine but I cannot update/commit and it says I need to "upgrade working directory".</p>
  
  <p><img src="https://i.stack.imgur.com/4Aii3.png" alt="enter image description here"></p>
  
  <p><img src="https://i.stack.imgur.com/4235c.png" alt="enter image description here"></p>
  
  <p>When trying to "upgrade working directory", it complains about a "missing default entry":</p>
  
  <p><img src="https://i.stack.imgur.com/jOeeN.png" alt="enter image description here"></p>
  
  <p>Does anyone know what's going on?</p>