Horrible job Nails. I don't know why they glue carpet down in the first place. It shouldn't be necessary, unless maybe it's a thin cheap one.
But anyway.......... the glue could be either water-based or solvent-based. Probably solvent.
Try and remove all the hairy bits, just leaving the glue itself.
Do what the others have suggested. Scraping mainly.
Also, chemical paint strippers, or even rent a power scraper.
Do be careful with Doogie's heat gun though. Old solvents are highly inflammable ;o)