In order to downgrade ATI Catalyst from 13.4 to 13.1 it leaves behind some OpenCL drivers, and reinstalling does not solve the issue.

Here is the solution

If you have installed a newer Catalyst version ever and go back to an older Catalyst, OpenCL uninstall will not remove all OpenCL files and this could cause your OpenCL to be in a broken state.

– uninstall opencl(64).msi (available inside c:\amd\support\ in one of the subfolders)

delete those files under c:\windows\system32 & c:\windows\sysWOW64 if you are on x64:

SlotMaximizerBe.dll
SlotMaximizerAg.dll
amdocl.dll
OpenCL.dll
OpenVideo.dll
OVDecode.dll

and this folder:

C:\ProgramData\AMD\KDB

– restart and install opencl(64).msi again from c:\amd\support\ in one of the subfolders)

– restart again, now “AML Device Install” will re-create the proper OpenCL database

Source post here

You can verify by running GPU-Z that OpenCL is checked off.

I also had to run Driver Sweeper

I also tried this article on removing the stuff.