ERROR Unexpected exception: sys.nframe()

I developed a shiny-app, which is working fine most of the times. But in some cases I am getting an error, where the app crashes. In the rsession-logs this message appears.

ERROR Unexpected exception: Error occurred while calling sys.nframe(); LOGGED FROM: int main(int, char* const*) C:\Users\Administrator\rstudio\src\cpp\session\SessionMain.cpp:3429

Can anyone help me to understand that error-message and maybe aswell a way to prevent it?