Occasionally. Error is exactly as the return says: ERROR max no of 100 conversations exceeded.
Probable cause is either too much parallel load through IS / B2B server, or long running RFC/BAPIs, but check with your SAP Basis to make sure all is OK in R/3.
Best solution is probably to design error handling and retry process for this particular error. Our method is normally to log to database with specific status after an error like this, then a scheduled service runs regularly, selecting a list of transactions to be retried and loops through list re-running RFC/BAPI service.
If you have defined a connection pool of more than 100 connections in the SAP Adapter and really need that many parallel connections, then you have to set the environment variable
set CPIC_MAX_CONN=xxx
in the environment, where the IS is started.
You may also need to increase the gateway parameter gw/max_conn
on R/3 side (T-code SMGW → GOTO → Parameters → Display).
But I don’t think, that any application needs that many parallel connections. You should make a review of your application and then decrease the connection pool a bit.