Help! Part will knit together but will not form solid

Hey all

I'm new to the forum I wanted to use this place as a last resort, my part is mosty boundary surfaces with a few surface-lofts, ( I plan to turn the body into a solid first, then the handle) I manage to knitt them all together. But When I select the "try to form solid" option I get the error. " Cannot knit a surface to itself. Please choose more surfaces or faces."

Have I missed a step somewhere?

SolidworksSurfacing