Yeah, most likely the first theme to use it did not use the "load" option, which gave you the opportunity to select the wrong file to load.

I would find a working theme with a command box (like austerity) and use !NetUninstallModule for each version of xlabel that doesn't work. (eg, !NetUninstallModule xlabel-2.8.5) When you switch to a theme that uses it, be sure to choose "xlabel-###.dll" if it asks which.

Themes should be designed so that it doesn't have to ask, but oh well. If you have the time, bug the theme authors about it later.