OK a complete deinstallation followed by a reinstallation fixed it

Hi 
The best way to revert back to eval version is to remove the line starting with "LIC0" from Tools.ini file.
Hopefully it will save you the time in future.

Hello Ullrich,

Thank you for using the Keil tools for Arm.

For posterity, take a look at

• the second step in the answer of this knowledge base article LICENSE: Web Error Code 2129 When Uninstalling a License
• Or this article: LICENSE: C9555E and R208 Error After Uninstalling LIC

Just be aware: if you are using MDK-Lite, there are some restrictions that come along with it. See GENERAL: MDK-ARM Lite: Creating commercial products

Good luck with your project

Detailed instructions now are summarized at:

"Returning to an Evaluation version of MDK (MDK Lite)"

   http://www.keil.com/support/docs/4163.htm

Kevin B said:

Just be aware: if you are using MDK-Lite, there are some restrictions that come along with it. See GENERAL: MDK-ARM Lite: Creating commercial products

So when did that change??

It used to be specifically stated that use for commercial projects was allowed.

EDIT.

The Product Page (and the restrictions page linked from it) makes no mention of this new limitation: