Thanks for the answer, at some point i had that quite figured out myself. The real problem behind this error is a little bit more though. Once i had the MemUnit_T thing figured out after a little expirementing, i decided to give the whole thing a try with R2013b and it worked like a charm. Apparently the ST Blocksets don't work with R2014a (yet?). It fails to copy almost all of the necessary .h files from the toolbox folder to the code generation target directory. That's what caused my initial issue aswell as the following ones.
little sidenote: KEIL uVision v5 works but you need to adjust several Flash- and Debugsettings. You're probably better off with version 4 at the moment.
tl;dr do not use a release higher than 2013b with the STM32F4 blocksets and go for uVision v4, not 5. that should solve most of the upcoming issues