Please Help Page Not Found.

I have a drupal site up and runing for a few weeks and everything seems to be going great. I was doing some updates and i needed to build some pages. So i created the page just like i have done before but when i add the line to the page to a menu or try to access the page i get

drupal The requested page "/~My Site/?q=testpage" could not be found.

I thought it had to do with the 7.17 to 7.19 core update but after i updated the system it is still happening?

i have read some posts that it happens when the Admin menu module is enabled. I unchecked the module but its still not working.

any help on this would be great.

thanks