Once upon a time, someone had the idea to use ‘_svn’ for a Windows SVN sandbox working folder instead of the standard ‘.svn’.
I suppose, that the idea was to use a more Windows-aligned folder name.
By using TortoiseSVN, it was quite transparent.
Years passed, and the idea was dropped, and these sandboxes aren’t working anymore by default.
TortoiseSVN still provides a hidden registry setting to support them.
Honestly, I don’t like the idea to edit the registry for something that one day may be ripped away.
To fix them, you simply have to rename ‘_svn’ folder to ‘.svn’.
What can go wrong?
The main problem here is that you cannot use Explorer because it doesn’t accept ‘.svn’ as a valid folder name.
At this point, you need to do it by Command Prompt, maybe with a small script like the following one:
cd %1 attrib -H "_svn" ren "_svn" ".svn" attrib +H ".svn" cd ..
If you have to fix several sandboxes into a folder, you can write down, a similar script like this one, to convert them all.
for /D %%i in (*) do call dotsvn1.cmd "%%i"