You should be able to click on Ignore to get past this error.

The software should then come up and display Tournament Setup.
Double click the Pool Play event in the Master Event List then click the Options button.

Choose an option in the "If odd number of Teams and Games" dropdown. If that dropdown is not active, click on "Number of Games each Team Plays" then select something in that dropdown.
Click OK. Click OK again. Click Yes.

Hopefully that takes care of the issue.

If you still have problems, you may want to create a new tournament and start over.