Problem Description:

When running c# form program, vs prompts an error: an unhandled exception of type “system. Argumentexception” occurs in mscorlib.dll

Problem solving:

The debugging window prompts the following error:

The savefile method of RichTextBox control is used here. For specific usage, see c# richtextbox.savefile method code example – pure sky (vimsky.Com).

To add @ in front of the path to prevent escape, the problem is solved.