I see that you found my
post as well.
My testing showed the following:
valid SinceID alone: works
valid MaxID alone: works
ulong.MaxValue MaxID alone: works.
valid SinceID and valid MaxID: works
valid SinceID and ulong.MaxValue MaxID: fails.
I think my recommendation would be to change your Search.MaxID and Search.SinceID to a nullable ulong data type, and then you could not include them in the twitter search URL string when they are null. I would attempt this myself if I didn't have a big deadline
at the moment that I need to meet.