Cant build project

Using uVision 3.31 compiling "gnu\examples\blinky" project
When I change my project from "use gnu compiler "to "use Keil CArm compilier" in the "Select arm development tools" dialog
the project doesnt build which is expected.

I then delete the blinky folder and copy the original blinky folder (from backup) to the gnu\examples directory
I get the error msg below when I try to build the project.

Assembling Startup.s
Error : cant execute 'AS"
Target not created

I would think the project contains the original files and not influenced by my changing compilier option in the previous
project.

Also how do you change linker control string in linker options ?

Thanks