This looks like the user account used to access your database is being denied. Has the password changed or expired?
You are corect, the account was being denied. How that account got to be that way, however, I have no idea.
My instance of CSR is the default, locally installed version of MySQL with the standard account. There are no password complexities or expirations associated with the default setup. This just happened all of a sudden and then I could no longer run an report that pulled data from the CSR.
I did manage to fix this issue, though:
I manually stopped/started all of the McAfee services for ePO and CSR on the server and then this fixed the issue. I wish I knew a root cause, but have none, and there is very little documented on CSR and troubleshooting.