I would have the users that are unable to print envelopes check to make sure that the settings in both the driver and application match exactly.
If you are still having issues after trying these steps, I suggest that you call into our support department for assistance @ 1-800-821-2797 or 1-800-835-6100.
When some people in our office try to print envelopes it says " resources required", others can print without an issue. how do we fix this problem?