What's the adress you are trying to send to , maybe it's really invalid and if the adress don't exist Blockchain.info will simply won't let you send your Bitcoins to it of course
1KgUmG9p2zdp5bgR47MHzu1cwuURJn1LwV
https://blockchain.info/address/1KgUmG9p2zdp5bgR47MHzu1cwuURJn1LwVWhenever i try to add new address, change label, or do anything.
It says: Checksum not validate.