When you attempt to start (launch) a Creative Suite 4 (CS4) or Creative Suite 5 (CS5) application, you receive the error "Licensing for this product has expired", "The serial number you used to activate this product has expired", or "Invalid serial number. The serial number appears to be invalid".
This can occur after the application has already been running successfully for some time, or when you start it for the first time.
There are three situations that can cause this error:
If licensing has expired for a CS5 application, the application will prompt you to enter a new serial number. When prompted for the serial number, enter the number from your purchased product.
The error "The license for this product has expired" is unrelated to the error "Licensing for this product has stopped working". An expired license means that a serial number, which is no longer valid, is still stored in the pcd.db database file. The valid serial number you received with your purchased product didn't overwrite the expired serial number during the installation process. Removing the expired serial number either by setting the computer clock back and erasing the stored number through the Deactivation menu, or by deleting the pcd.db file will allow you to enter your valid serial number.
The error "Licensing for this product has stopped working" is related to the activation component of Creative Suite 4 software, specifically to a problem with the FlexNet Service. (Creative Suite 5 software uses a different activation component.) See these documents for solutions on how to resolve this particular error: