Writing File to Temp Folder

The Path class is very useful here.
You get two methods called

Path.GetTempFileName

Path.GetTempPath

that could solve your issue

So for example you could write: (if you don't mind the exact file name)

using(StreamWriter sw = new StreamWriter(Path.GetTempFileName()))
{
    sw.WriteLine("Your error message");
}

Or if you need to set your file name

string myTempFile = Path.Combine(Path.GetTempPath(), "SaveFile.txt");
using(StreamWriter sw = new StreamWriter(myTempFile))
{
     sw.WriteLine("Your error message");
}

string result = System.IO.Path.GetTempPath();

https://docs.microsoft.com/en-us/dotnet/api/system.io.path.gettemppath

You can dynamically retrieve a temp path using as following and better to use it instead of using hard coded string value for temp location.It will return the temp folder or temp file as you want.

string filePath = Path.Combine(Path.GetTempPath(),"SaveFile.txt");

or

Path.GetTempFileName();