No luck if you manually load the subtitle either?
[Crtl]+[L]
Could you open the subtitle file with Notepad or Wordpad and copy e.g. the first three sub-lines here?
Which filters are shown under
(rightclick) > Options > Filters > Advanced?
Did you place your subs in the subtitles folder/directory as defined by you or in the same folder as moviefiles?
Possibly your settings prevent you from seeing that the (original) file-extension is (e.g.) .txt? The result of your renaming would then be that it actually ends with .srt.txt now, so that the file-name itself no longer matches the name of the corresponding avi.