Error message when opening form in Form Designer

In one of the documents we migrated from TB2 we got the following error message when opening any of the forms in Form Designer:

ORA-0001 Unique Conraint violated...

ORA-00001: Unique Constraint (WT_VP.TB_GN_CONTROL_P) violated.....
'insert into TB_GN_CONTROL(....)'

The form opens in Form Designer but adding a control and saving the form caused Administrator to crash (basically with same message).

I was able to solve the issue but I'm not 100% sure which of the following steps actually did the trick:

1) 1 ClickMaintenance
2) Re-Open project in Administrator
3) Duplicate an existing form

I did all three of them but I believe 1 Click Maintenance was not enough. Either you need to make sure to re-open the project afterwards or you need to insert an new form (I accidentally clicked the wrong button and the form got duplicated - and then the problem was gone....).

Map 2013, SP2