I've had to change my username on my host, and I'm getting an open basedir error instead of my blog. Folks on Sitepoint have always come through for me before, so I thought I'd post here and see if someone can help me out!
I've corrected the db info in wp-config, and have checked the siteurl etc in the options table.
But I have an unknown file trying to access the lib according to the OLD path
Warning: Unknown: open_basedir restriction in effect. File(/home/myusername/.../index.php) is not within the allowed path(s): (/home/myOLDusername:/usr/lib/php:/usr/local/lib/php:/tmp) in Unknown on line 0

Warning: Unknown: failed to open stream: Operation not permitted in Unknown on line 0

Fatal error: Unknown: Failed opening required '/home/myusername/.../index.php' (include_path='.:/usr/lib/php') in Unknown on line 0
A simple testfile on the same subdomain works just fine.
Maybe it should be obvious, but it's not to me. Can someone who's more familiar with WP please point me in the right direction?