Problem with \includegraphics - file not found!

\graphicspath does not really setup directories. graphics (or graphicx) only adds the given strings before the file name of the mandatory argument of a \includegraphics, tries to open the file and if is successful uses this concatenated file name to include the file. So

\graphicspath{{C:/Users/felix/Desktop/Bachelorarbeit/TeX/BA_text2/images}}
\includegraphics[scale=1]{gap_v3_v4_AT.png}

would try to load C:/Users/felix/Desktop/Bachelorarbeit/TeX/BA_text2/imagesgap_v3_v4_AT.png (note the missing slash before gap_v3_v4_AT.png). If C:/Users/felix/Desktop/Bachelorarbeit/TeX/BA_text2/images is the name of a directory, you should append a slash at the end:

\documentclass[12pt]{report}
\usepackage{graphicx}
\graphicspath{{C:/Users/felix/Desktop/Bachelorarbeit/TeX/BA_text2/images/}}
\usepackage[a4paper]{geometry}

\begin{document}
\includegraphics[scale=1]{gap_v3_v4_AT.png}
\end{document}

In this example graphicx will try to load C:/Users/felix/Desktop/Bachelorarbeit/TeX/BA_text2/images/gap_v3_v4_AT.png.

BTW: \includegraphics does not need a figure environment. figure environments makes sense only, if LaTeX should move the figure if it could not be printed in place. Mostly figure without \caption makes no sense.

1. You can try to finish your \graphicspath statement with a double slash (//)
2. Check the path that you registered in \graphicspath. Many times the file doesn't compile because of a small typo. Try to copy and paste the path from the properties of the file.