Hi Stephen,
Typically, you should not make changes to files and directories in 'matlabroot'/toolbox.
The basic way to fix this is to reinstall MATLAB. But If you can find the original copy of 'griddata.m', you can replace yours with that one. You can type
>>which griddata
on the MATLAB command prompt to see where it should be located.
Generally it should be located here: 'matlabroot'\toolbox\matlab\sparfun\gmres.m
Then run
>>rehash toolboxcache
to update the search path and cache file.
Good luck.
