svn Error when commiting-Access denied: 'foobar' MKACTIVITY MYREPO:
The svn_activity log is higher level and typically not as good for debugging these problems as the lower level http methods, e.g. MKACTIVITY. 403 means forbidden, usually this is due to an authz access file but can also come from rules in the apache config. If you can attach the apache config for the problem repository and the authz file we can probably figure it out.
Look for a directive like this in your config files:
AuthzSVNAccessFile /data/authz