Yeh seems its software publisher trick ...
but as you can see on that topic :
After 30 days it asks again for the serial number.
Enter your serial you'll get a message: License file is corrupt.
Delete your license in user/all/eplan/common and enter the serial number again.
Now it will work for 30 days again.
This is not a comfortable solution, but it works.
anyway with emulator you can unpack protected program and then patch api calls ....