C# Error CS1504 – Source file ‘{0}’ could not be opened — {1}

C# Error

CS1504 – Source file ‘{0}’ could not be opened — {1}

Reason for the Error & Solution

Source file ‘file’ could not be opened (‘reason’)

A source file could not be opened or read by the compiler. The file may be locked by another application, or there could be some other operating system problem. The message includes the operating system’s reason for why the compiler could not open or read the file.