Ok this was annoying…I had an older trial version of the standalone Flex Builder 3 on my system (Mac 10.5) and wanted to activate it with a new serial for FB3 Professional.
Whenever I entered the serial in “Help -> Manage Flex Licenses” I kept getting a message saying “Invalid serial number” even though it was a brand new serial. Damn.
Mark gave me the original hint to remove the license.properties file under /Library/Application Support/Adobe/Flex but FB wasn’t re-creating it when I entered my serial on startup. I needed to create the file manually and enter my serial number. These steps got me going:
- cd /Library/Application Support/Adobe/Flex
- sudo touch license.properties (create the file)
- sudo nano license.properties (edit the file)
- enter the following “flexbuilder3=xxxx-xxxx-xxxx-xxxx-xxxx-xxxx” (where xxx etc is your actual serial)
- restart Flex Builder
Also thanks to 62five.com for the post.

2 Comments
THANK YOU! after a few weeks back and forth with Adobe support this thing is finally working. i will make sure to send them this link.
Hi mate,
Thank you so much for this invaluable info!
I’ve been having the same issue, where, once FB 3 was updated (once it was a trial), entering my valid serial number did not work!!
I tried many methods to resolve this, but thanks to your advice, I was able to get it up and running with a breeze!
Thanks heaps.
Kind regards
Mili.