https://bugs.winehq.org/show_bug.cgi?id=50756
--- Comment #19 from Alex Folland lexlexlex@gmail.com --- That leads to this at line 3322 of ntdll/unix/file.c in the definition of nt_to_unix_file_name:
if (!name_len || !IS_SEPARATOR(name[0])) return STATUS_OBJECT_PATH_SYNTAX_BAD;
So, it looks like because the path doesn't start with a separator (and I'm guessing this means a slash or backslash), its syntax is considered invalid for the conversion. I researched this a tiny amount and found https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-even/c1550f9... which states that NT object paths must start with "??". This is all just a guess too, but it sounds like to me that in your example, the NT object path should be like this before being passed into nt_to_unix_file_name_attr:
"\??\C:\Program Files\TortoiseSVN\scilab2\.svn\pristine\7f\7f67b1a3bd137585d365a2098253c3519f198f98.svn-base"
I wonder if stupidly prepending "\??\" or "??" somewhere would give us a hint.