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L166: Fatal Error 250 (Code Size Limit...)

Information in this article applies to:

  • C166 Version 4.01 or later


I have the full professional version of C166 and yet when I link I get fatal error 250. What gives? I have tried reinstalling the software, but it hasn't helped.


There are some problems in the version 4 install program that may lead to the installation of a "restricted" toolset.


  1. Download the latest updates from but do not install.
  2. Completely remove the tools from your computer.
  3. Delete all the files and directories installed (the default is C:\Keil and all its subdirs). It will warn you about "impacting registered programs"; you may safely disregard this message.
  4. Run the install program from the CD or from the download.
  5. Choose "Install Software" not "Install Eval Software".
  6. A little later in the dialog, the install program will ask for your name and company info, and it'll have another field for serial number, which will have "Eval Software" in it by default.
  7. Delete the Eval Software serial number and and enter your serial number, dashes and all, and put the add-on disk into your drive.
  8. The install should proceed without problems.

When you apply the latest update, you must go through the normal installation process and enter your serial number.

This process should leave you with a FULL version of the tools, troubled no longer by the Fatal Error 250. If a licensed installation still reports error L250 with C500 warnings, then the release version may be outside of the product's support period. Either renew support, to access the latest upgrades, or downgrade the installation to a supported version. Earlier releases are available from the download section, Maintenance Status and Previous Versions.



Last Reviewed: Thursday, February 25, 2021

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