The Neopost AS225 is a 5-head fixed head printer. The driver itself has been known to have issues reporting the proper paper size, which leads to instances where nothing can be printed from any software program. To correct this, do the following:
In the Print Settings window, select the Neopost AS225P as the printer.
In the Template pull-down menu, select the "Envelope #10.lbx" template.
Click on the Edit template button.
In the Label Designer, click on File>Page Setup.
Click Print Setup.
Change the printer to the "Address Printer 5" printer driver that should be installed from the Neopost CD-ROM.
Set the paper size to #10 envelope. Ensure that the orientation is set to landscape, so the 9.5 inch edge is going from left to right.
Click OK to exit Print Setup.
Click OK to exit Page Setup.
Double click the detail bar.
Enter 3.75 in the Height window that appears. A #10 envelope is actually over 4 inches tall, but the driver reports it as 3.8.
Click OK.
Close the template and save your changes.
Print!
The address block must be positioned on the template from top to bottom in the position of the heads that your AS225 is using (the upper 2.5 inches). If it's not correct, you can move the address block to a new location until you determine where the heads are pulling the data from.
The AS225 driver itself is quite a quirky beast, so the setup itself is quite tricky. Once set up properly, however, it should present no further issues.