Hi Rohit,
Looks like an intermittent connection error, Check on following steps:
1. Check if sm59 destination for IDOC RFC is working from all application servers.
2. Check NWA if the JCO is running and connects to ECC Client using PI central Server gateway information.
3. Check if ECC IDOC RFC destination is also using the correct Gateway, it should point to PI Central Gateway server if not default.
Regards,
Nipun