It only happens when I got on the server craftedmc.dmch.nl
this is the bug report

1. A fatal error has been detected by the Java Runtime Environment:
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2. Internal Error (os_windows_x86.cpp:149), pid=6772, tid=6860
3. guarantee(result == EXCEPTION_CONTINUE_EXECUTION) failed: Unexpected result from topLevelExceptionFilter
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4. JRE version: 6.0_31-b05
5. Java VM: Java HotSpot(TM) 64-Bit Server VM (20.6-b01 mixed mode windows-amd64 compressed oops)
6. An error report file with more information is saved as:
7. C:\Users\Mika\AppData\Roaming\.minecraft\hs_err_pid6772.log
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8. If you would like to submit a bug report, please visit:
9. http://java.sun.com/webapps/bugreport/crash.jsp
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   AL lib: (EE) alc_cleanup: 1 device not closed