ERROR 000816: The tool is not valid

Error Message

When running a script tool as a geoprocessing service, the tool fails, and returns the error message:

Error:   
ERROR 000816: The tool is not valid.

The tool runs successfully in ArcMap and ArcGIS Pro, and does not display any extended error information in the ArcGIS Server logs.

Cause

The script tool contains third-party modules unrecognized by ArcGIS Server.

Solution or Workaround

ArcGIS Server utilizes the 64-bit version of Python. For any module not part of the core Python installation, ensure a 64-bit version of the module exists. For more information, refer to ArcGIS Server: Deploying custom Python packages for ArcGIS Server.

To install and import modules, follow these steps:

1. Launch Python Command Prompt, and enter the following line:

cd C:\Python27\ArcGISx6410.x\Scripts

2. Install the module by running the following:

pip install <module_name>

Note:
If these modules cannot be recognized, upgrade pip. To upgrade pip, launch Python Command Prompt, and navigate to C:\Python27\ArcGISx6410.x. Run the 'python -m pip install --upgrade pip' command to initiate the upgrade.

3. Import the newly installed modules. Refer to ArcGIS Server: Test custom Python packages for services published from ArcGIS Desktop for steps to do this.