Ok, i've been an idiot, but now i got it to work.
In glVertexAttribPointer i passes as "size" (second parameter) the size of the array in bytes.
However it does expect the number of components of the attribute (1,2,3 or 4). And due to some tests, the code that also contained "glGetError" was commented out, which meant, that i didn't see the "invalid value" error, that GL threw at me.
Thanks for all your help and clarifications!
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