The devtestlic.xml file resides in the DEVTEST_HOME folder of where the Enterprise Dashboard is running.
To verify whether your license has expired, open the file and look at the <validuntil> value and make sure it is not earlier than the current date.
If your license has expired, please open a new CA Support case.
When opening the case:
Indicate in the Title the Version of DevTest the License is for.
Indicate in the Description the full error you are getting.