i actually resolved the errors i got, but i don't know where they came from.
The Problem was:
After I updated to the recent drivers and sdk-files, my kernels didn't work anymore. I got a "-14" error on my waitForEvents (CL_EXEC_STATUS_ERROR_FOR_EVENTS_IN_WAIT_LIST), so i checked the CL_EVENT_COMMAND_ EXECUTION_STATUS, which sometimes was "-59" (CL_INVALID_OPERATION). i checked my operations twice, re-included the headers and so on. after i removed all the code, except for the "header", i figured, it had to be sth with the header, which it was:
i changed a "__constant" variable to a "__global" variable and: tadah, it worked.
the entire kernel-"header", that ceased to work was:
__kernel void RGB2LAB(__constant uchar4 * inputImage1, __write_only image2d_t outputImage)
the constant in question is similar to the one in the box-filter-example. i don't remember, why i had changed it from global to constant.
so: any ideas? i'm just curious (so: no rush), but maybe someone else has a problem like this, too.