When you have this error message in the BIOS '19a - voltage mismatched', this is because you have a non-refresh board. It will never go this error message as the non-refresh is not meant to work with 45nm processors. So unfortunately, there is no fix for this. At least your one is working, in some cases it does not boot at all.
Even upgrading the bios, it wont make the error message disappear.
One thing only to be 100% sure, check the pba number of the your board if it is non-refresh board and if your cpu is 45 nm.
From the website below:
Your cpu is a 45 nm manufacturing technology as all the Xeon 5405 are 45 nm. So definitely it wont work, sometimes if it works, you are left with an error message in the bios '19A'.
Recap: 65 nm cpu works fine with non-refresh board and refresh board
45 nm cpu works fine with refresh board only
Other than this, i dont have any suggestions.
Refresh board has a 'R' at the end.
Useful website to check: