Winamp 5.20 introduced a new feature, that could mess with GTSdll.
To be more specific, it could be that GTSdll does not display the song you are playing, but some different one. Also it won't be able to display tags like album, genre or tracknumber. To fix that you'll need to set the correct directory in GTSdll Settings.

(this screen appears on winamp 5.2 installation)
If you select
Shared settings for all users you'll need to set the winamp Directory in GTSdll settings to the installation directory of winamp.
Usually
C:\Program Files\Winamp\If you had GTSdll installed before, you probably don't need to change anything.
But if you select
Seperate settings per user account you need to set the directory to
%appdata%\Winamp.
Usually something like
C:\Documents and Settings\USERNAME\Application Data\Winamp\ on Windows XP
and something like
C:\Users\USERNAME\AppData\Roaming\Winamp\ on Windows Vista.
The
red part ~usually~ needs to be replaced by the name you use to log on into windows. It can differ!
To be asolutely sure, right click on your "my documents" folder, and check the path in there.