This appears to be an issue that goes way back. I started setting up my new store yesterday and suddenly I couldn't create new categories, move the current ones or delete categories. Now all I get is the message "You cannot add categories until we've completed your previous request." It's been 24 hours and everything is where I wanted it to go. I searched google and found people experiencing this error for quite a while now. I couldn't find a fix on the user side. I'd really like to be able to create categories again...
