Unusual situation (not sure how it happened) but... Participant received $500,000 distribution FIVE years ago. Original 1099R indicated entire distr. as eligible for rollover, which participant did. Now determined that $100,000 of the distribution was not eligible for rollover and should have been reported as TAXABLE distribution five years ago. Are there 1099R rules that deal specifically with reporting in this situation? How does one deal w/ the mandatory withholding at this late date? Thanks in advance for any info/suggestions.