User can't log in with new account, but I can?

Hi

One of my new users is having trouble logging into his new account. I user buddypress and membership, and he's registered with a 2 word log in id and capital letters ie John Smith

When I try to log in using the username and password he sent me, it works. But he's adamant it doesn't on his PC.

What could be the issue here?

He says he's definately typed the username and password in correctly (even to the extent of copy and pasting) but still no joy.

Thanks

Sally