Something seemingly so simple ....
When running a query I wanted to be prompted for whether the records should show those with a Checkbox field Ticked, eg (T)rue, Unticked (F)alse or Both Ticked and Unticked (All)
To cut directly to the chase, here is the query criteria which I finally got to work.
Note: The checkbox field being queried is called TaxClaim
IIf([Tax Claim? (T)rue, (F)alse or 'Enter' = All] Is Null,[TaxClaim],IIf([Tax Claim? (T)rue, (F)alse or 'Enter' = All] Like "T*",-1,0))
If Then Else
If Nothing is entered in the prompt dialog e.g. if just 'Enter' or 'OK' is pressed Then display everything in the [TaxClaim] field ... both Ticked and Unticked.
If anything is entered in the parameter dialog (preferably T, or True, or F, or False) the Else statement is executed.
Within the Else section is another nested IIf which checks if the entry is Like anything starting with T (Like "T*") if it is Then it sets the TaxClaim query criteria to -1 which equates to ticked checkboxes. If its anything Else which doesn't start with "T" (i.e. F or False) the TaxClaim query criteria is set to 0 which equates to Unticked checkboxes.
The first and subsequent references to the one prompt must be identical
The only thing which returned All records (both ticked and unticked) was the use of the Field Name (TaxClaim) in its referenced form (square brackets [TaxClaim])