This is the error:
Is there a way to generate a new .csproj or fix it or do I have to create a new project and import everything into it?
The file is likely to be corrupted. Unfortunately the best solution is to create another project from scratch and include the files.
From the original project file you can see what files you need - not just C # code, but also resource files and other formats, if they exist. The more complicated it is to get references - try opening the corrupted .csproj file in a text editor and finding out which references it uses, so you can rebuild them.