I had the same problem (fresh install). The table dtregister_group_amount has two fields missing (examount and examountfor) which means the record is not created in this table for a registration. I created these fields manually (I have guessed at decimal 8,2 for the type) and it all works correctly. Could someone please advise the correct types for these fields. I believe the file dtregister.xml should be altered to create these two fields on install.
..but i believe this is the solution to the original thread. If you check your table dtregister_group_amount, I bet you will find your fields missing too, add the fields and hey presto, it will work.
This has now been resolved. Please download 2.1.4 again from your account on this site. It also includes one other non-related fix. Anyone having this issue needs to have a download of 2.1.4 from AFTER 1/16/08 2:55 PM (EST). Thanks.