Running both instances BitCoinCore - Mainnet & Testnet altogether

Hello Everyone,
Is it possible to run both instances of BitCoinCore - Mainnet & Testnet altogether on Windows Server? Currently Bitcoin Core (Mainnet) is performing some download. At this point while running testnet instance showing an error - "unable to start http server. see debug log for details"

Looking at debug.log showing up -

2017-12-07 11:52:42 Binding RPC on address :: port 18332 failed.
2017-12-07 11:52:42 Binding RPC on address 0.0.0.0 port 18332 failed.
2017-12-07 11:52:42 Unable to bind any endpoint for RPC server
2017-12-07 11:52:42 scheduler thread start
2017-12-07 11:52:47 scheduler thread interrupt
2017-12-07 11:52:47 Shutdown: In progress...
2017-12-07 11:52:47 Shutdown: done

Till the time mainnet is downloading i want to work through testnet. I looked at bitcoin.conf for both environments - it seems like mainnet is also using similar port.

Please suggest. How to proceed.

Thanks In Advance.