I am an IT Administrator running Exchange Server 2007 sp1 on a Server 2008 box.

Somehow the IIS details for OWA got deleted. I have now managed to get it all working again and OWA works a treat, but our company BlackBerrys don’t seem to want to communicate with OWA. The BlackBerry internet service returns the following error message:-

“An error occurred during email account validation. please check your information and try again.”

I have tweaked and changed and rechanged about every setting in the book.

I have one blackberry which gets email via BIS from a Box like yours.
However, it uses imap. But it works.

Not all BIS version support exchange 2007 using OWA

here:
View Document

is a walktrough from rim regarding BIS and Exchange OWA

All our company BlackBerry's worked fine until IIS7 got nuked.
Our company BlackBerry's are currently with Orange and Vodafone.