I was getting an Index Out of Bounds error and I finally figured out how to fix it. Seeing that others occasionally get this as well, I thought I'd post here in case it helps others.
In TexGen you can type in the Units Per Pixel box and it will let you type values that don't appear in the list. In my case, I was typing 8. However, the Alpha version has the text '8.0 (1440p)'. You need to select that from the list - if you just type 8 into the box the code in the backend can't find that value in the list and gives the error.
Suggestion - you might want to limit that dropdown to only allowing a selection and not allowing typing.
Thanks for the great program!