I just opened a MS Word file created in 2003 with Pages v4.3 on Mountain Lion. That file was not created on Blackboard. I see your profile suggests you remain on Lion. Is that accurate?
Blackboard strongly suggests Word documents created in Office 2007 or later be uploaded as .doc, rather than .docx, for backward compatibility with older versions of MS Word. Pages can handle the 2007 and newer .docx format.
Blackboard, on the other hand, has very strict guidelines about copying/pasting content from original MS Word files, as this embeds artifacts that corrupt documents posted on Blackboard. They require the use of the Blackboard formatting toolbar. The files submitted to Blackboard must have closed, legal character file names with specific three-letter extensions.
You may be attempting to access a corrupted MS Word file created by misadventures within paragraph 2. If that is the case, the problem originates from the source, and not Pages.
Blackboard document guidelines
Blackboard site.