The disks can be PC or S50 formatted before use with Sdisk. Maybe you really have a damaged file or a format that the S50 won't load (S550, W30 or S700)
There is a S550 to S50 converter at Roland page: http://www.rolandus.com/SUPPORT/SOFTWARE/PCSAMP.HTM
You'll find the Roland Library online at the Sgroup page: www.generalconcepts.com/sgroup

Mgomes