Elaine,
Most of the CRC errors that I have experienced with 2900s are due to auto-sensing speed and duplex across links. This may or may not be your problem, but I would nail down most of your speed/duplex settings if you haven't already. I do not know of any documentation on CRC errors and what the upper limits and such would be. The rule of thumb we use here is that we first clear the counters on the switch and then take our measurement, if over the next 1-3 minutes see more than 10-ish we will begin troubleshooting. Usually our first step is auto-sensing. I do not recall a crc error that was not caused by either an auto-sensing, or bad port problem on either end. I hope this helps...
-Bo
