License key information is stored in your model assembly, so at run time that assembly must be found and loaded so that the license can be read. This validation is done first thing, so that various features can be turned on or off as needed.
You should re-generate your model following a DevForce upgrade. Open the Object Mapper, and then choose to save and regenerate all files. This will ensure that the license (as found on the development machine where DevForce was installed) is used to "stamp" the model assembly.
Next ensure that a probeAssemblyName element contains the correct assembly name of this model assembly. Also double check that the assembly is located in the bin folder.
If it's still not working after all this, check the Debuglog.xml to see if there's anything helpful there, and either post it here or send it to support if you still need assistance.