No, I'm not kidding. My old 83752B Synthesized Sweeper has thrown this error today. It powers up, runs all self-tests and begins restoring instrument state, then crashes with the error Firmware Hurl! and an Exception 40 message.
I'm assuming this means something in flash has become corrupted but the only ways I can see to restore the instrument to factory settings involve using the front panel keys, which obviously doesn't work from where we are now.
We don't have resources available to us to help you, but if you can provide the related 3-digit error code, we can come closer to understanding the problem.
Of course if you can come up with the sevice documentation that would help too.
In the meantime, you may want to invoke a full self test - and here are the steps (from the Installation and Quick Start Guide):
1. Press the following keys: PRESET (hardkey); SHIFT (hardkey); Special (softkey); 21 (hardkey); Hz/s/ENTER (hardkey). The right portion of the display shows: Full Test NOTRUN 2. To run the self-tests, press Hz/s/ENTER (hardkey) again. The display shows flashing asterisks as each test is run. When the instrument passes all the tests, the display shows: Full Test PASSED. If the instrument fails a terst, the display shows the title of the failed test. If the instrument fails more than one test, the test title shown is the most significant failure. 3. Either press PRESET (hardkey) or cycle the AC power after the full self-test is complete.