The send buffer that the Informix connectivity network module allocated is less than the minimum DRDA required size, which is 512 bytes, or more than the maximum size, which is 32,767 bytes.
Check the sqlhosts file on the Gateway computer. If the send buffer size is configurable through the sqlhosts file, make sure that the send buffer size is configured to be from 512 bytes to 32,767 bytes, inclusive.