Symptoms

The project cannot be updated due to the error: DocumentFormat.OpenXml,Version=2.5.5631.0,culture=neutral,PublicKeyToken=31bf3856ad364e35 is not a valid assembly name issue.

Cause

The issue is related to the missed assembly dependency on the host where the project is being updated.
Assemblies are added on the .Net References tab of the batch type properties, project properties or Document Definition properties. All classes of the added assemblies are available in scripts and global modules.

There are two types of assemblies available within FlexiCapture:

1. Standard assembly name (represent standard system libraries and libraries provided by other installed software like Microsoft Office that have already been added to the system and can be added to FlexiCapture by specifying their names)
2. Assembly files (can be added by browsing the file)

In case the Standard assembly is used, it has to be present on the host where the project is being updated. If the assembly is missed for any reason (OS reinstallation, etc.), the XXXX is not a valid assembly name issue error will be shown.

Resolution

The error above shows the issue with the Open XML SDK V2.5 assembly missed in the project.
In order to fix the issue, the Open XML SDK V2.5 has to be installed on the problematic host where the project is being updated.

Please keep in mind, that for the changes to take effect, it is necessary to restart the program.

Additional information

External assemblies 

What is a Standard Assembly?