[DanCooper]

Then I started the new version, added 3rd Rock as a source & got the following message:

I've to look what's wrong with that, but has nothing to do with your actual problem.
 

I ran the program again & proceeded as you instructed.
Anyway, here is my log: https://pastebin.com/GViKZjuQ

Your log is:

Code:

TVDB Premiered enabled: "True"
TVDB Premiered raw value: "Tue-09-Jan-96"
TVDB Premiered returned value: "Tue-09-Jan-96"

TMDB Premiered enabled: "True"
TMDB Premiered raw value: "Tue-09-Jan-96"
TMDB Premiered returned value: "Tue-09-Jan-96"

NFO builder: "TVDB"
NFO builder TVDB raw value: "Tue-09-Jan-96"
NFO builder new value: ""
NFO builder: "TMDB"
NFO builder TMDB raw value: "Tue-09-Jan-96"
NFO builder saved value: ""

My log with the same tv show and your settings is:

Code:

TVDB Premiered enabled: "True"
TVDB Premiered raw value: "09.01.1996"
TVDB Premiered returned value: "09.01.1996"

TMDB Premiered enabled: "True"
TMDB Premiered raw value: "09.01.1996"
TMDB Premiered returned value: "1996-01-09"

NFO builder: "TVDB"
NFO builder TVDB raw value: "09.01.1996"
NFO builder new value: "1996-01-09"
NFO builder: "TMDB"
NFO builder TMDB raw value: "1996-01-09"
NFO builder saved value: "1996-01-09"

First thing we can see: both scrapers returns a value.
Second: you got another date format than me. But that's not really true because i used the function "ToString" to log the raw value what changes the "DateTime" value to a date based on your Windows system settings (my one is European style)
Third: both scraper results reach the NFO builder that put together the data from diffrent scrapers
Fourth: the NFO builder tries to convert your date to the default style yyyy-MM-dd and fails (NFO builder new value = "")

Why it worked on your old PC? I think you used another country/date time setting on Windows or another Windows version that handles the date different.

In the TVDb scraper i used "Date.ToString" and saved that as result.
In the TMDb scraper i used "Date.ToString" and than a try to convert it back to a "Date" object in the format "yyyy-MM-dd" what is nonsens. As fallback the Date.ToString value will be used that is "Tue-09-Jan-96".
In the NFO builder i try again to convert it back to a "Date" object and that fails again with an empty result that will be used.

So, .NET can convert a Date to "Tue-09-Jan-96" but it not able to convert it back to a "Date" object... that makes no sense at all.

I think the solution is to convert the "Date" directly to "yyyy-MM-dd" in the scraper, that should work also with "weired" system language settings. Tomorrow i will release a new version with some other fixes, i hope than it works again.