Gulp EPERM: operation not permitted using MSBuild

I am trying to integrate our build server with our angular build. Locally the build work perfectly but when I try and run the build on the build server I am getting the following error:

RunGulp:
Running gulp task dev
  gulp
  [08:35:38] Using gulpfile C:\Builds\10639\TCC.NET\1.Development CI\src\TCC.W
 eb.Client\gulpfile.js
 [08:35:38] Starting 'default'...
  [08:35:38] Starting 'build'...
  [08:35:38] Starting 'js'...
  stream.js:74
        throw er; // Unhandled stream error in pipe.
        ^

EXEC : error: EPERM: operation not permitted, open 'C:\Builds\10639\TCC.NET\1.
 Development CI\src\TCC.Web.Client\public\app.module.js' [C:\Builds\10639\TCC.N
ET\1.Development CI\src\TCC.Web.Client\TCC.Web.Client.csproj]
      at Error(native)
C:\Builds\10639\TCC.NET\1.Development CI\src\TCC.Web.Client\TCC.Web.Client.wpp
.targets(14, 5): error MSB3073: The command "gulp" exited with code 1. [C:\Build
s\10639\TCC.NET\1.Development CI\src\TCC.Web.Client\TCC.Web.Client.csproj]

I've looked at some various posts on the error and they mostly revolve around permissions issues but the public folder and the app.module.js files have the correct permissions.

I am not at all familiar with gulp so looking for some other ideas on things to check.

Solution

My issue turned out to be the readonly flag on the files being built.

Found a solution here