When using Firefox 3.5 or Chrome browsers, you or your students may get an error message that says "Please enter a valid file." This only occurs when uploading files in the assignments tool . It does not effect the SafeAssignment tool. The way to get around this error is to use IE 7 or older versions of Firefox to upload assignment files.
This has been reported to Blackboard and we're hoping for a fix soon. This is another reminder that, as fast as browsers are changing these days, it's a good idea to tell students that if they have a problem with Blackboard, to try using a different browser. Blackboard has a list of supported browsers that you can refer them to.