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MSB3249 diagnostic code

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This article describes the MSB3249 error code.

Message text

MSB3249: Application Configuration file 'value' is invalid.

Remarks

The error MSB3249 is raised by the ResolveAssemblyReference task in MSBuild when an invalid or malformed application configuration file (for example, app.config) is detected during the build process. This usually occurs when the configuration file contains syntax errors, invalid XML, or unexpected values that prevent MSBuild from properly resolving assembly references. See ResolveAssemblyReference task.

Possible causes

  1. Malformed or invalid XML: The app.config file contains syntax errors or is not well-formed XML.
  2. Missing or incorrect <runtime> section: The app.config file is missing the <runtime> element or contains invalid data in this section. See <runtime> element.
  3. Unrecognized configuration settings: The file includes settings that are not supported or are incorrectly specified.
  4. File not accessible: The app.config file is missing, locked, or inaccessible due to file permissions.

Resolution

  1. Validate the app.config file:

    • Open the file in an XML editor or IDE that supports XML validation.
    • Correct any syntax errors or invalid XML structure.

  2. Check for unsupported or invalid settings:

  3. Ensure file accessibility:

    • Confirm that the app.config file exists in the expected location.
    • Ensure the build process has the necessary permissions to read the file.

The ResolveAssemblyReference task is responsible for resolving references to assemblies during the build process. An invalid app.config file can prevent this task from completing successfully. For more information on the ResolveAssemblyReference task, see MSBuild ResolveAssemblyReference Task.

Related content

ResolveAssemblyReference task

Applies to

All versions of MSBuild