I agree, you should try uninstalling Express and then reinstalling. Make sure that you are disabling any Anti-Virus software when you uninstall and reinstall.
What OS are you using?
I don't think that the file is missing. With most OS types, this particular dll, if missing, will get recreated. The fact that you are getting an invalid operation message steers me in the direction of a file associated with this driver is missing, which a reinstall will fix or a registry setting for Outlook Express.