I have no doubt that you will solve this problem.
Please be extremely careful as you do, so that you can come back here and tell us what it turned out to be!
I believe that we can benefit from your situation. It will give weight to some step in the process everyone uses, explicitly or implicitly, in error hunting.
It may well not be your problem, but you can tell from the tone of the replies here that > 99.44 % of the time it is you.