Invalid shares ?

If you get any invalid shares it means you may have few ethminer windows or even rigs with the same hashrate, if yes dont use the same value in mining address.
For example you have two miners with 60MHash, you need to put 61@ADDRESS and 60@ADDRESS.
Hashrate is mainfactor to generate shares with unique difficulity, it's also internal indentifier regarding miners on your address.
If you misconfigured it, some shares may get rejected. But if you still getting invalid shares even if you have valid settings, and you are not trying to lower target in ethminer to cheat us.
Then just contact us!