Were you able to resolve this? If so please come back to this thread to update it so others can benefit from the solution. From the information given my best hunch is that the softphone configuration needs to be checked. Make sure your settings match this screenshot and that everything else is configured as detailed in the ADTRAN Softphone Configuration Guide
If all of the settings in the guide have been double checked and you are still having the issue I would need to see the current 7100 configuration along with the output of a debug sip stack messages and debug voice verbose both enabled at the same time while the issue is recreated. You can submit those to the FTP server with the instructions below.
Open Internet Explorer web browser on their PC
Type the following URL: ftp://ftp.adtran.com
Press the Alt key, click View, and then click Open FTP Site in Windows Explorer
Double-click the "Incoming" folder
Drag and drop files from PC into the Internet Explorer window
Reply to this post with the exact filenames used so we can retrieve the files
Not able to resolve it. I will double check the settings, but they should not have changed from when it was working. I will gather the debugs as soon as I can
Go Figure...Tested it again this morning and could not get it to fail. Other than time, nothing has changed on the 7100 or the PC. If the problem happens again, I will gather these debugs and update this thread.
Thanks for the update.