Page Ranking Forums Strange happenings, why

[googlejoe]

I run and have run a few forums with attaced web pages.

Set up 2 phpbb forums (test and high traffic) both indexed within days and ranks on google tool bar, yes even the test one

Set up 3 SMF forums (test, low traffic and high traffic)
They have been up for around 15 weeks, this is the wiered bit the low traffic forum is showing on the google tool bar ranking as 1 but the high traffic forum rates zero. abour 4 posts a day on the low traffic forum and 400 on the high traffic one.

Any ideas ?