one project plays back "brokenly" with heaps of static, pops

basically my c5.52 is rock solid. never crashes, no dramas, works like a charm! c6 dont get me started… anyway, so i went to work on an old track that i started months ago that i never had any problems with.

firstly, it didnt open properly, closed c5 restarted it and it opened fine. press play and it plays in short burst the track with heaps of static, pops, crackle- which i cannot work with obviously. it exported and played fine.

i have had a similar problem with this before when i have a track in c5 playing and audio in windows it would clash and have the same effect. this was due to the sample rate, if i recall correcly which once changed, played both audios back over each other perfectly. is this a similar problem?

has anyone else encountered this?

please help.