That is normal from blockchain.info's end to counter double spend attack towards the network.
but if i have 100 btc in my wallet,
and i send 10 to someone
why can't i send 10 btc to someone else immediately?
si there a way to get this done?
Because bitcoin works differently. When u r sending 10 BTC out of 100, it might be that u r actually sending 99 BTC where 89 BTC is coming back to your address. blockchain.info does not know about as they dont store your data. they do all the calculations on the fly. hence they wont allow.
u wont probably face this problem on coinbase because they store your data including private key. hence they are not a recommended wallet service.