@loopz this person seems to have fixed a similar issue
Bug - Failed to locate an existing game cache for Oldschool Runescape
I'm not certain if this is an issue with the cache that's at (for me) "C:\Users\Me\jagexcache" or the cache at (for me) "C:\Users\Me\.jagex_cache_32"
Do you know where yours is?
Edit: I think this issue is when Runemate is looking for the first one I mentioned, jagexcache. Though I'm not completely certain.
Apparently cache directories are expected to be at the following (for windows):
%USERPROFILE%\jagexcache\runescape\LIVE
%HOMEDRIVE%.jagex_cache_32
%WINDIR%.jagex_cache_32