Question : "You cancelled the previous operation error" MS ACCESS

Help!  I have no idea what the hell is going on.
I copied a main form "Turnin Maint" as "Turnin Entry", and a subform "TurninDetail Maint" as "TurninDetail Entry". The following code works fine in the "Turnin Maint" form, but will not work in 'new' "TurnIn Entry" form. For reference I have included original code as well as 'new' code:
Current code line from "Turnin Entry" form:
[Rate Per Sig] = DLookup("[Fee Per Sig]", "Petitions", "[Petition Code]=Forms![TurnIn Entry]![TurninDetail Entry].Form![Petition Code]")
Original Code line from "Turnin Maint" form:
[Rate Per Sig] = DLookup("[Fee Per Sig]", "Petitions", "[Petition Code]=Forms![TurnIn Maint]![TurnInDetail Maint].Form![Petition Code]")

Answer : "You cancelled the previous operation error" MS ACCESS

Are you absolutely sure that the Subform OBJECT on your main form is named TurnInDetail Maint? Note that this would NOT the name of the form being used as a subform, but instead the name of the Subform Object being used on the mainform.