The version may be why. There were some big changes with 5.1.0 that can cause problems with backwards compatibility. Message names are one thing that changed and css class name are another. You could try going through the tiddlers and making sure all message names start with tm- (I think it was tv- before but I am not certain. And all css classes that start with tw- should be changed to start with tc-. One again, I am not certain if it's tw-, hopefully someone else can confirm.
There may be other differences but those two are the most common problems I have seen with older modifications.