Both MacWrite II and ClarisWorks WP provide incorrect margins when choosing Envelope - Edge Fed in Page Setup... from the LaserWriter driver. The default margin settings will cause the application to return an incorrect margin message when attempting to print.
Correct (Minimum) margin settings for edge feed envelopes:
Top: 4.42
Bottom: 0.25
Left: 0.43
Right: 1.46
This is not an issue for ClarisWorks Graphics documents which is the recommended environment for creating envelopes.