Lou, a GFCI device on the primary side of a transformer will not 'see' a ground fault on the secondary side of the transformer. A ground faulted secondary will only cause a larger line to line current on the primary side.
Assuming a grounded system on the secondary side a ground fault on the secondary will just loop back to the grounded phase / neutral of the transformer.
Thanks Bob, I thought as much but wasn't sure.
So the OP's problem is on the primary side.