I\'m using TortoiseSVN. I just made quite a few changes to my working copy and now I went to do a commit some of the files went through but at one file named Search.aspx.cs
I had similar kind of issue "(Can't open file 'folder.svn\tmp\text-base\file.svn-base': The system cannot find the file specified")."
It was not because of case-sensitivity issue. But because the file path was too long. So I renamed the folder with a shorter name and moved it right inside C Drive and checked in successfully.
So if it is not case sensitivity, please watch for length of the full path to the file as well.