Date of 1900?

Anyone try to work with a date of 1900? We have an expense report that someone entered 1/1/1900 by mistake, and the expense report has been approved and posted. When allocating, this item kicks out as "Rate Not Found". When I try to correct it as an execption in the Alloc Multi-Level Rate Entry screen the program will not accept the date 1/1/1900, leaving the field blank. Does anyone know how to get the date to be 1900, or how to change an expense report that has been posted already although not allocated? It is stopping my entire project from being allocated. Thanks.