Quoted from machine.slave

no idea about getting the ink off the plexi, but my guess is that the ink / vinyl peeled due to moisture build-up.  I wouldn't worry about printing it on vinyl if it's going under plexi anyway, just regular paper would work fine (since the plexi will make it look glossy regardless).  Printing on regular matte paper at the print shop should bring your cost of reprinting down significantly.

Hope that helps.