admincp goes missing

I've just installed vbseo and I must say it looks great!
Unfortunately, the next time I went to my admincp and did a logon, I was redirected back to my site's index page.
Please note, I can get to admincp log in page, but once I enter my admin name and password and click login, I land up at site index page.
Modcp works fine, so far only admincp is having issues.

Any ideas?

Thanks.