After playing with it a bit further, I too encountered this. After some investigation, it looks like it's a formatting error.
If you manually enter in each team number on the team list tab, the cells are formatted incorrectly and you will get this error. Hence, you need to copy/paste in a team list from somewhere else.
If you manually enter in the team #'s on the matches tab, then double click the match number, you see that in the 'notes' section you have your team #'s right aligned, whereas the original copy has them left-aligned. You also cannot double-click the team here or on the matches page to automatically go to that team's tab. The workaround for this one is to copy each team # cell from the team list tab over to the matches tab. Then it works perfectly.
Starting with the original, if you manually enter team numbers (e.g. 1130) for a new match, you will get an error that says the team is not found in the team list. This furthers my suspicions that all of the VLOOKUPS look at formatting.
Ok, so some bugs, and some workarounds, but I still like it
