Please check your settings for Tolerance groups once again.
Ensure that you specify sufficient amount in the fields Amount per document and Amount per open item account item.
While posting the document through FB50, if you specify more amount than the amount which you specify in tolerance group settings, the document will not be posted.
Hope this helps..
Supose you have a blank(empty)tolerance group for your CoCd and did the rest configuration IMG>Financial Accounting (New)....Define Tolerance Group for Employess. Then you must Assign User/Tolerance Group (your sap ID) to the blank(empty) tolerance group in the
|Tolerance Groups Menu|