Yep, grid itself doesn't show up.
As far as filters on Step 3 of 9 in the Grid Wizard:
Field:Vendor = [vendorname] (actual Type In the vendors name); and then some OpportunityStage filters. All roles can view. Nothing in the Advanced Screen settings. The only thing I can think of is that a few of the grid fields (Advanced Link) have some SQL statements. But, I would think if there was something wrong with those, it wouldn't show up on their portal either. But it is fine there.