Thanks so much for replying.
My webhost support deleted the entire plugin folder and the blogs now work. I know plugins are very troublesome, but I never would imagined them causing this type of problem. I'll need to post an update once I find the culprit plugin.
Meanwhile I had set up the new blog I was trying to launch under my other WPMU install to try to get it going (this one uses subdomains).
Couple of issues I'm still having:
1) I am having image referencing problem. After uploading images through media uploader the files seem to upload, but don't show online (even within the uploader).
I'm not exactly sure how to test the permalinks. I do seem to have a referencing problem with images. The image URL shows as this, but leads to 404pg:
http://4everyoungmbs.milehighcentral.com/files/2010/03/testimonials.jpg
Uploader reference URL: http://blog.domain.tld/files/year/month/image-file
My permalink setup is /%postname%/
Upload path is wp-content/blogs.dir/5/files
Do I need to add something to htaccess to account for this so images display?
2) I added a page named "Links". When viewing the page here, it goes to an Apache "index of links" page outside of my website:
http://4everyoungmbs.milehighcentral.com/links/
Another htaccess referencing issue?
I really appreciate your help! I see you on here a lot...I don't know how you keep up with this forum, but you are invaluable :)