UMS console shows an error message like "Unexpected end of input stream found at ..." during registration of thin clients.
Thin clients cannot register with UMS over a remote link via VPN gateway, router, firewall or other networking device due to issues with large packets.
The error may occur even if there is no NAT used and the networking device seems to be configured correctly so e.g. pinging is successful in both directions.
Please consult the documentation for your network device and look up the options for handling large packets. In the case of SonicWall devices the solution is setting the Ignore Don't Fragment Bit option.
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