I think I may have misspoken. This is what the help file says:

"Some publishers produce puzzles which cannot be solved with logic but need guessing or trial-and-error.

Solving a puzzle with a guess is not as satisfying as solving a puzzle with logic and reasoning.

For a computer, trial-and-error puzzles are easy. It is just a matter of blasting the puzzle with every possible combination of numbers. Teaching the computer to use logic is a more difficult thing.

Trial-and-error puzzles are not often found in print. However, they are very common among puzzles on the Internet.

There is a blurred area between logic and guessing. There are some extreme techniques which can pass as logic, but which involve making multiple assumptions until one of them proves right or wrong.

Technically these can be called valid puzzles, but at Pappocom we regard them as unsatisfying and unfair.

This program knows how to solve and verify these unfair puzzles, but it does not allow them to be included among its own original puzzles."

I agree that a forcing chain (that does not require more than one assumption) is an extension of techniques like X-wing and Swordfish. I assumed that only those puzzles requiring multiple assumptions were what the program flags as invalid. I don't know if that's a correct assumption or not. I also associated the statements above with the term "forcing chain." Attribute that to the fact that I'm a newbie and still learning the lingo...

So... back to the puzzle in question... Can it be solved with logic?