Unable to write the output of custom tool 'tool' to file 'file'. <reason>
The project system could not write the output of the custom tool to the specified file.
Provided that the file name of a custom tool's input remains unchanged, the output from a custom tool is written to the same file. This error occurs if the generated output is locked on disk.
To correct this error
Restart Visual Studio and rerun the custom tool by right-clicking the affected file and selecting Run Custom Tool from the shortcut menu.
The generated file is probably out-of-date, because the project system could not update it.