Maya 5 Dynamics HELP

Hey guys,
I was working on a small project today with particles. I modeled a tub and a shower head. I created particles so they would act as water falling from the shower head. I want to keep the particles within the pool, so I select the particles and the object I want it to colide with… the tub. But then I get this error: “Error: Particles can collide only with a NURBS surface or polygonal surface. Select the particles, Shift-select the surface, then select Particles > Make Collide.”.

The tub was modeled in NURBS, so I don’t understand why it’s not recognizing it. I also tried to convert this object to Polygons, yes still no luck.

Please help