That is strange; the AgentClassesV section is before the SkillsV section of the data.000 file, so I wouldn't have thought a problem editing skills would cause an error there...

Can you restore the original, unedited data.000 file and load the save properly?
If so, then try the hex edit procedure again, being more careful. If not, then the problem happened before the editing started, so you should check your next most recent save, to see if it loads ok.