This error can result from trying to run MATLAB 6.0 (R12) with an MATLAB 5.3 (R11) or older dongle. Make sure you are using the MATLAB 6.0 (R12) dongle with MATLAB 6.0 (R12).
If you are using the MATLAB 6.0 (R12) dongle and still receive this error, send your license.dat file (from $MATLABROOT\bin\win32) and a brief description of the problem to MathWorks Technical Support. Note that $MATLABROOT is your root MATLAB directory.
NOTE: If you are attempting to run MATLAB R12 on Windows XP with a dongle, this configuration is not supported. While not supported, this configuration may work with a modified dongle driver. See the related solution 1-18YBS "Why do I have problems installing MATLAB R12.x on Windows XP with a dongled license?" for more information.