Please help me with compiler error.

I was developing a project in Unity, and decided to browse the asset store. Upon browsing I found an audio asset. I imported the files, and having never used audio files I tried to drag and drop one of them into the scene. When I tried to run I got:

Internal compiler error. See the console log for more information. output was:
Unhandled Exception: System.UnauthorizedAccessException: Access to the path “C:\Users\Playcool\Documents\FPS Beta - 1\Temp\Assembly-CSharp-firstpass.dll.mdb” is denied.

at System.IO.FileStream…ctor (System.String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, Boolean anonymous, FileOptions options) [0x00000] in :0

at System.IO.FileStream…ctor (System.String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, Boolean isAsync, Boolean anonymous) [0x00000] in :0

at System.IO.FileStream…ctor (System.String path, FileMode mode, FileAccess access) [0x00000] in :0

at Mono.CompilerServices.SymbolWriter.MonoSymbolWriter.WriteSymbolFile (Guid guid) [0x00000] in :0

at Mono.CSharp.SymbolWriter+SymbolWriterImpl.WriteSymbolFile () [0x00000] in :0

at Mono.CSharp.SymbolWriter.WriteSymbolFile () [0x00000] in :0

at Mono.CSharp.CodeGen.Save (System.String name, Boolean saveDebugInfo, Mono.CSharp.Report Report) [0x00000] in :0

at Mono.CSharp.Driver.Compile () [0x00000] in :0

at Mono.CSharp.Driver.Main (System.String args) [0x00000] in :0

How do I fix this?

The .mdb file in the first line of the error has somehow had its file access permissions changed to read-only. You need to locate the file, right click it, go to properties, and ensure “Read Only” is unticked.