I have License Manager Error -15 although I have my own license file.

I have License Manager Error -15. My OS is ubuntu 12.04 and installed matlab r2013b. But it shows error message.

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License checkout failed. License Manager Error -15 MATLAB is unable to connect to the license server. Check that the license manager has been started, and that the MATLAB client machine can communicate with the license server.

Troubleshoot this issue by visiting: http://www.mathworks.com/support/lme/R2013b/15

Diagnostic Information: Feature: MATLAB License path: /home/ubuntu/.matlab/R2013b_licenses:/home/ubuntu/Documents/MATLAB/licenses/license.dat:/home/ubuntu /Documents/MATLAB/licenses/network.lic Licensing error: -15,570. System Error: 115

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I installed matlab at /home/ubuntu/Documents/MATLAB and license file is in the same directory. (I have my own license file so I put the directory address when I install matlab.

At first, matlab worked well. When I run my code at matlab, somebody put the on/off button so the computer was offed. After that, when I execute matlab, it shows error message. I deactivated license file and uninstalled matlab and installed it again, it has same problem.

I saw http://www.mathworks.com/support/lme/R2013b/15 but it wasn't helpful.

How can I solve this problem?

Help me.