texxs on "406 error"

I'm getting error 406 when trying to login to a wordpress website. I have several other WP websites on the same machine. I'm having this problem with non of the others. It was working fine yesterday.
I tried the:

<ifmodule mod_security.c>
SecFilterEngine Off
SecFilterScanPOST Off
</ifmodule>

.htaccess fix and it did nothing.
I see the login page and using the proper password (it was saved by browser)
The front end of the web site looks fine
I check out the database via PHPMyAdmin and there's still only one user (don't really know what else to look for)
It was working just yesterday and now this. Have I been hacked? How do I fix this?

Thanks all.