I think you problem in certificate store. please do the following:
- run mmc
- menu file/Add Remove Snap-In
- from the treeview select certificates, than select radiobox Local computer
- Certificates(local computer)/Personal/certificates
- look through all certificates listed there. there should be a dublication. (if the duplication is not visible right on the first look, double click on each certificate, go to Detatis tab, find the Subject property)
Get rid of duplication if possible. in other case define FindByThumbprint criteria in your config