I found this solution in another forum, and it has seemed to help a lot of people:
Quit the VZ access software.
(1) Launch a terminal app ( hyperterm or equivalent ) and select the serial port that represents the Pantech 4G modem.
(2) type "at" (without the quotes) to make sure the modem responds OK (it may or may not echo your typing, i.e it's blind typing)
(3) type at+cgdcont? and save that list for future reference
(4) Type at+cgdcont=1,"IPV6","vzwims","0:0:0:0:0:0:0:0",0,0
(5) type at+cgdcont? and make sure the command in 4 "stuck"
Close the terminal port. Launch the VZAccess software and try to connect.
The fix to the WMC604 Error for VZ Access Manager is::
1. Unplug the Broadband card and close VZ Access Manager
2.Right Click on My Computer and choose manage
3. Click Service and Applications
4. Click Services
5. Click on "VZ Config Service" and stop the service...Click apply then Ok
6. Right Click on the VZ Config service and click properties
7. Click the log on tab and check "Allow Service to Interact with Desktop"
8. Click Apply and Ok.
9. Restart the VZ config service. Click Apply , Ok
10. Close Services and try connecting with the Card again.