Looking over the support pages for the 6204, I have renewed concerns that the Crucial RAM might be the problem.
The latest version of the BIOS is dated 29-10-2003.
From the age of the hardware, it is possible that Crucial has made an error in the memory chip density that is compatible with your system. (Note: The error could be in PBs documentation.)
Comparing your old 256MB DIMM with the new 512MB DIMM, does the new DIMM have twice as many memory chips on it?
If the new DIMM has the same number of memory chips, and especially if it has fewer memory chips, it might have too high a memory density for your system.
Unless the new DIMM has twice as many memory chips, I would complain to Crucial until they send you RAM that is compatible with your system.
Chas