Hi Ashish,
Is there any existing instance running on server with instance no: 00 ?
If yes, then installation can't move ahead by selecting instance 00 for ASCS. You can go ahead by selecting any other instance no. Once the instance installation get complete, you can modifiy the sapms<SID> in services file to 3600, so you ASCS message service can run with 3600.
But we have to make sure there is no other instance running with port 3600.
Regards,
Anil