I just deployed code last week without a problem.  When I run all tests in the sandbox, I get 85% coverage and no errors.  However, when I try  to deploy anything from my sandbox, I get the following error on 3 of my test classes:

System.DMLException: Insert Failed. First Exception on row 0; first error; Duplicate_Username, Duplicate Username, <br> Another user has already selected the username <br> Please selectd another: [Username]

Each test class does create a user object and even though I have deployed these before without problem, I modified so they hae a differeint email address.... However I still cannot deploy.

I don't believe I have made any changes to the live org but I cannot deploy... any ideas? thanks!!!

Fred