Add specific error message for failed address checksum.

ui/app/send.js

@@ -262,6 +262,11 @@ SendTransactionScreen.prototype.onSubmit = function () {
     return this.props.dispatch(actions.displayWarning(message))
   }
 
+  if ((util.isInvalidChecksumAddress(recipient))) {
+    message = 'Recipient address checksum is invalid.'
+    return this.props.dispatch(actions.displayWarning(message))
+  }
+
   if ((!util.isValidAddress(recipient) && !txData) || (!recipient && !txData)) {
     message = 'Recipient address is invalid.'
     return this.props.dispatch(actions.displayWarning(message))

ui/app/util.js

@@ -37,6 +37,7 @@ module.exports = {
   bnTable: bnTable,
   isHex: isHex,
   exportAsFile: exportAsFile,
+  isInvalidChecksumAddress,
 }
 
 function valuesFor (obj) {
@@ -66,6 +67,12 @@ function isValidAddress (address) {
   return (isAllOneCase(prefixed) && ethUtil.isValidAddress(prefixed)) || ethUtil.isValidChecksumAddress(prefixed)
 }
 
+function isInvalidChecksumAddress (address) {
+  var prefixed = ethUtil.addHexPrefix(address)
+  if (address === '0x0000000000000000000000000000000000000000') return false
+  return ethUtil.isValidAddress(prefixed) && !ethUtil.isValidChecksumAddress(prefixed)
+}
+
 function isAllOneCase (address) {
   if (!address) return true
   var lower = address.toLowerCase()