SymptomsYou get error message when trying to use Modernbill v4 license:
NOT OK (Your license key is not valid for this version of ModernBill. Please generate a new license key.)
ResolutionThis usually means you have very old Modernbill version or your system was moved from one server to another. To get this issue fixed you need to perform upgrade to the latest v4.4.2 version.
Please contact support to obtain the distribution files.
Please, backup you fileset and database prior to upgrade.
Make sure your system meets all requirements
Note, you cannot upgrade directly from 4.0.2 to either the latest v4.
Here is the upgrade path:
4.0.2 to 4.1.5
4.1.5 to 4.4.2
Once upgrade is finished, login to the members area and copy your license key to newkey.php file and place this file in the root of Modernbill directory. Follow instructions on the login page.