I have had, and continue to have, similar problems with Index issues. I have about 42,000 people in one of my family files which I have not been able to open for some months. At each attempt,it appears to go through the validation process OK but, at about 20% of the way through compiling the Index, matters come to a jarring halt. I suspect that the file is probably corrupted and that this may have been caused when I went through the process of compiling relationships. This was done pretty much immediately before the hiccup arose.
Initially, I was not unduly concerned because I had two backups to fall back on. The first of these, however, turned out to be of no use at all, as it was a replica of the data on the hard drive. Consequently, I was unable to open this file. The other backup was about three months older and contained less data. Although it would mean losing a few months work, I decided to give it a go. Much to my amazement and horror, on attempting to open it, the same problems occurred.
A few years ago, I uploaded my family file which then contained about 26,000 people to RootsWeb. As I had run out of options, I decided to download this via a Gedcom file and have now included all of this data in a separate family file which appears to be working OK. The sad thing about this of course is that I have lost about three years work and I am 77 years old with a heart problem.
Like you and many others I have had a great affection for Generations and have been using it since it first came on the market under the name of "Reunion". However, in light of the fact that it is no longer supported, and clearly has issues with recent versions of Windows, I have decided to abandon it in favour of Legacy 7.5 which I have justpurchased.
Although I should have no difficulty in importing a Gedcom file of the 26,000 people into Legacy, it would be much better if I was somehow able to import the 42,000.
As a possible means of accomplishing this, I was heartened when I read your posting, particularly the final paragraph. When I tried this, the file opened but when attempted to open the Index nothing came up except for a message which said that there was not enough RAM allocated for the purpose.
If I can't get to the Index to hopefully identify and correct any corrupt data, then I am at an impasse.
Any help or suggestions you might care to offer about these issues would be most appreciated.