I installed Reader XI very recently, but this problem is affecting my Adobe Acrobat X Standard. Every time I start the problem, AVAST snags another .api file. Even when it doesn't, Acrobat crashes after a few seconds. I've tried repairing Acrobat twice, but it didn't help. Reader XI seems to be working okay (at least it runs), but then it was Acrobat I needed to use so I didn't test it much.
A full scan by AVAST and a quick Malwarebytes scan found nothing. I left a full Malwarebytes scan running when I left home this morning, but I'd be very surprised it it found anything.
Frustrating to say the least.