I also had the same problem, with TMax 100, as Dave states. It was a test in bright sunny conditions, bracketed. I shot again with Ilford FP4, great results. There was also another post in the last few months describing the same experience (TMax100, I think, but I'm not sure).
The only thing that rings a bell to me is reading about the TMax films when they were first released (Fred Picker, I think) and the warning that the 100 speed film was verrrry "responsive" to developer variation.
Sandy - any ideas?