Error 91 is a data corruption error for the Sunplus.mdb. You can perform a rebuild on the database: http://help.salontouch.com/solution/articles/14000030917-perform-database-rebuild.
Other errors that can cause this are Errors 3265, 3343, 3024, 3197, 3051, and 3056.
Some of the errors can be recovered from if the data structure is corrupt and not the data itself. A rebuild will resolve this issue.