At least Miranda has an advanced setting for compression.
The error most prorably occured due to wrong format of data I had sent to the server.
Anyhow the server should reply with
Where the condition seems to be just this undefined.
Perhaps the new version of rfc 3920, part 5.8, will allow this to be more precise.
Anyway, the compression code will be in XIFF as soon as it works.
Could you record the first message, as is, that is transfered between the client and the server, once the compression has been negotiated?