Assuming you have Windows, this should probably fix it:
Step1: Download this zip.
Step2: Press Windowskey + R
Step3: Type in %appdata%, press enter.
Step4: There should be a .technic folder, open it.
Step5: Open the hexxit folder, and the bin folder in your hexxit folder.
Step6: You should now be at \AppData\Roaming\.technic\hexxit\bin\
Step7: Open the jar folder in your zip file, from this folder, take the files
jinput.jar
lwjgl.jar
lwjgl_util.jar
And replace them in your \.technic\hexxit\bin\ folder.
Step8: In the \bin\ folder go to the \native\ folder. In the zip file, go to the \native\windows\ folder.
Step9: From the \native\windows\ folder, take all the files and replace the files in your \AppData\Roaming\.technic\hexxit\bin\natives\ folder.
Step10: This should have fixed the error, for more information, check here. These steps fixed the same problem for a friend of mine.
Also, please make sure that you have the latest version of Java installed on your pc!