I’ve found the following error regarding the opening of .fchk files in GaussView5.0.
CConnectionGFCHK::Parse_GFCHK() Missing or bad data: Alpha Orbital Energies Line Number 1234
The error is prevented to a first approximation (i.e. it at least will allow GV to open and visualize the file but other issues may arise) by opening the file and modifying the number of basis functions to equal the number of independent functions (which is lower)
FILE HEADER FOpt RM062X 6-311++G(d,p) Number of atoms I 75 Info1-9 I N= 9 163 163 0 0 0 110 2 18 -502 Charge I 0 Multiplicity I 1 Number of electrons I 314 Number of alpha electrons I 157 Number of beta electrons I 157 Number of basis functions I 1199 Number of independent functions I 1199 Number of point charges in /Mol/ I 0 Number of translation vectors I 0 Atomic numbers I N= 75 ... ... ... ...
Once both numbers match you can open the file normally and work with it. My guess is this will continue to happen with highly polarized basis sets but I need to run some tests.