When upgrading from 2.1 to 2.91, the revision error was encountered:
The INSERT statement conflicted with the CHECK constraint "CK_RECURRINGGIFTINSTALLMENT_VALIDDATE". The conflict occurred in table "dbo.RECURRINGGIFTINSTALLMENT". The INSERT statement conflicted with the FOREIGN KEY constraint "FK_RECURRINGGIFTINSTALLMENTPAYMENT_RECURRINGGIFTINSTALLMENTID". The conflict occurred in table "dbo.RECURRINGGIFTINSTALLMENT", column 'ID'.
Download and install the latest patch, which contains all fixes from previous patches. If you are running an older version, download and install the latest version and then the patch.