It could be a Java Runtime Environment (JRE) issue.
Try running the browser tune-up first. Please refer to
http://www2.blackboard.com/tuneup/ for instructions.
You might also try clearing the Java and Internet Cache.
To clear the Java Cache, go to the Windows Control Panel and select the Java icon. There's an option to clear temporary internet files.
Navigate to the Java folder from your hard drive: HD > Applications > Utilities > Java.
Open the Java Preferences application.
Click on the General tab.
Click the Delete Files button (under the Temporary Internet Files section).