We are a TPA and have been advised by our custodian who handles withholding and Form 1099-R reporting that an error in 2010 withholding can no longer be corrected since it's now 2011. I always thought this could be done by filing a Form 843, Claim for Refund and Request for Abatement and Form 941c, Supporting Statement to Correct Information. Then the excess 2010 withholding would be "refunded" in the form of a credit to the payor's account. But, maybe this is ancient history? The custodian says that at this time their Form 945 filing must match their total Form 1099-R filings and that "adjustments" are not allowed. Now I know the IRS can make rules that don't make sense but is that the case here? Mistakes happen and it doesn't seem right we cannot make the appropropriate corrections for the participant. Any ideas? Thanks in advance for your help.