RELIC:
The website info for the motherboard series says "Athlon-64/
Athlon-64 FX up to 4000+..."
That is general information for both version 1.x and 2.x; not specific information for each version.
You have a straight Athlon-64, not an FX series, going into a version 2.x board and the limit for yours is as I said above, according to the CPU approved list. It's in the 3rd file bundled in the zip file.
Anyway, don't feel too bad because marketing people make compatibility kind of complicated knowing there is a lot of money to be made from people making mistakes. Case in point would be the other people responding here without checking the approved list. You're lucky you haven't gone out and bought a new power supply, then some new RAM, followed by a new CPU fan and God knows what else may still be suggested...

The lesson is to always check the approved CPU list since it's compiled by the engineers and QA people testing those CPUs.