Hi Charles,
That message usually means that what is selected at the print driver does not match what is loaded. You said you since ran letterhead through and it worked, is there a possibility that that when going File > Print that the settings, paper type, and orientation aren't exactly matching how the tray is loaded? I found THIS SOLUTION from our KB that may also help you solve the issue.
Last week I was able to print #10 envelopes using the bypass tray of our 7835. This week, no such luck. I have made sure the envelopes are inserted correctly, flap side up. The bypass tray is selected for #10 plain white envelopes. I can get letterhead to go through the bypass tray just fine. When I try to pass an envelope, it does nothing and says "One or more queued jobs need resources."
I am using Word to print the envelope, the same as when it worked last week. All the print settings for Word are the same as last week as well.
Any advice on how to troublshoot this? I don't know what could have happened between last week and now.