Did you compile control_slip.vhd? That is the file where the CONTROL entity is described.
I'm not sure this is the correct syntax for an entity instantiation: U_CNTRL:entity CONTROL(CONTROL_SLIP), but as I'm not a VHDL guru I can't say for sure, but examples I've found online show something more like U_CNTRL : entity work.CONTROL
Besides this you've also included a component declaration for CONTROL along with the entity declaration? Either use one style or the other, I'm not sure what happens if you have both for the same component.