The error message seems odd, but we should assume that the line received from the remote server was containing "UD3" as the "method tag", then "UD3" again as the type of the "isSnapshot" flag, which was supposed to be "B".
The syntax for the "UPDATE BY MAP" command is, in fact:
<timestamp>|UD3|S|<item name>|S|<ID>|B|<is snapshot>|S|<field 1>|S|<value 1>| ... |S|<field N>|S|<value N>
If you are using LS .NET Adapter library for the remote part, this could be a bug or a strange communication issue.
Can you replicate the problem and check the actual content of the communication?
For instance, setting the "lightstreamer.adapters.remote.request_reply.NotifyReceiver" logging category to DEBUG level would produce the log of the inbound messages.
