I'm trying to finish a massive project and my cross dissolve transition has stopped working - all the existing dissolves on the timeline are fine but any new ones just won't work - premiere treats it like a cut!!!! New ones will work with GPU turned off but that's not gonna help with tons of AVCHD footage

Please any help???

You could clear out the Media Cashe database.

Crazy thing is - if I apply a 'Block dissolve' effect with all the parameters default (sort of null effect) to the preceding clip - the cross dissolve transition works!!! Mental!