InfoPath wants to create a Forms library, and if the ability to create the Forms library is not present, then it will error out and will likely create a regular document library be default. If this occurs in SharePoint 2010 you can activate the following feature at the site level (go to Site Actions > Site Settings > Manage Site Features): Team Collaboration Lists.
This feature allows for (amoung other things) the ability to create Forms libraries, so next time you publish InfoPath will create the Form Library and should not give you that error.