“Could not find a part of the path” error message

The path you are trying to access is not present.

string source_dir = "E:\\Debug\\VipBat\\{0}";

I’m sure that this is not the correct path. Debug folder directly in E: drive looks wrong to me. I guess there must be the project name folder directory present.

Second thing; what is {0} in your string. I am sure that it is an argument placeholder because folder name cannot contains {0} such name. So you need to use String.Format() to replace the actual value.

string source_dir = String.Format("E:\\Debug\\VipBat\\{0}",variableName);

But first check the path existence that you are trying to access.