Thanks for posting, @Wenke65. If you have already entered your full version of Creative Suite 5.5 serial number, could you please provide more information?
Why are you reinstalling the upgrade to Creative Suite 6 in 2026?
What happened to the previous installation?
Did you deactivate the previous software installation?
Several software errors can corrupt the licensing files, so once you have provided more details, @Wenke65, then others can provide you with better guidance.
When installing an upgrade version you must have BOTH the new program’s number AND the qualifying program’s serial number to enter during the install process