A transfer of PVsyst license for exemple from your old machine to your new machine is an operation that should be performed with care strictly following each step and providing correct information (all characters of your license key and customer ID). These information are available on the email from PVsyst Admin that followed the order of the license.
All the steps of a license transfer are documented in the following Video:
Here is the corresponding Video in case you are still using V6:
Important note in case you are using V7 and V6
: you have to transfer each license independently. You have to complete the transfer using PVsyst V7 then do the transfer again using PVsyst V6. You should not mix the two versions. For exemple, the transfer will fail if you start it on your old machine using V6 and complete it on your new machine using V7.