I don't know if this is a good thing or a bad thing

Googlebot has been really hammering my forum. I guess it's good because I have great placement for different types of searches. (Always on the first page, mostly the top 2 and many times #1)

One minor concern is google is about 25% of the daily bandwidth that is used. 

What I'm really concerned with is I get on the average of  20-30 error message PER HOUR from googlebot (ID'ed from the IP addy)

Errors like this for example:

Personal Messaging is only for members

http://www.mysite.com/cgi-bin/yabb2/YaBB.pl?board=&action=imshow 

or

Sorry, this service is for registered members only!

http://www.mysite.com/cgi-bin/yabb2/YaBB.pl?board=&action=viewprofile 

I tried different things with sitemaps and robot.txt and the problem seems that the bots don't understand the highlighted part

Without giving a reason for applying for membership we cannot process your application.

http://www.mysite.com/cgi-bin/yabb2/YaBB.pl?board=&action=register2 

I tried

<a href="http://www.mysite.com/cgi-bin/yabb2/YaBB.pl" rel="nofollow">login2</a> 

in /default.html which of course shows up as links on the forum.

I'm stumped, any ideas that would help?

Thanks

I guess I just hate seeing error messages 

If I log 200 error messages, 180 of them would be from googlebot, which makes it difficult to view if there are any problems I may need to deal with.

I can't see any upside of googlebot trying to sign in as a member a few dozen times in a single morning.

I average about 450,000 page views a month. I'm not unlimited, but I barely use 15% of my allotted bandwidth per month.

Thanks Captain, I'll give it a try and see what happens.

Blocking the googlebot dropped me from the top 2 position down to #8 

I hate to unblock the IP but I dislike not having a high ranking more

Any other tips?

Googlebot visits me very seldom although we are also #1 if you search for "silent hill forum". If a googlebot is on, then it's never more than one at the same time. Could be because of my robots.txt, but I don't know if it's really working. But somehow I manage to prevent my forum from being flooded by bots