hex nut_ai in my toolbox might be corrupted.. i have never saved over it and it is read only, but it has stopped working for all of my files. 

When I open it read only I get the attached errors. I do not really want to fix and save as new because this is read only.. If i save new I am sure I will need to go through and update every single file. 

Any suggestions? Can I repair the toolbox? I have not done this before, if anyone knows how it would be very much appreciatedToolbox