Looks like opencl cannot allocate enough memory. This happened to me quite some times when mining normal scrypt.
Close all applications (Especially chrome/firefox), shutdown cgminer and start it again.
It also helped me to set the intensity lower in the config to make the startup faster. Then I slowly push the intensity to max
Here is my current config for a HD 7950, getting up to 200 kHash/s
I guess other 7950s get more. mine is pretty low clocked
{
"intensity" : "12",
"vectors" : "1",
"worksize" : "256",
"kernel" : "scrypt",
"lookup-gap" : "4",
"thread-concurrency" : "0",
"shaders" : "0",
"gpu-platform" : "0",
"gpu-threads" : "1",
"no-pool-disable" : true,
"queue" : "1",
"expiry" : "60",
"scan-time" : "60",
"scrypt" : true,
"shares" : "0",
"kernel-path" : "/usr/local/bin"
}