When latex fails to make a pdf-file out of your latex-file it can be hard to find the error in the latex-file.
Use of [fragile]
on ordinary frames results in
Runaway argument? ! File ended while scanning use of \next. <inserted text> \par <*> undervisning_med_R.tex I suspect you have forgotten a `}', causing me to read past where you wanted me to stop. I'll try to recover; but if the error is serious, you'd better type `E' or `X' now and fix your file. ! Emergency stop. <*> undervisning_med_R.tex *** (job aborted, no legal \end found)