Error code 1403901 occurs when a user or client program attempts to perform forbidden file upload or download operations. These operations may be forbidden because either:
The user is not permitted to perform the operation at all, or
The status of the task or processes does not permit the requested operation at the moment.
There are two kinds of file attachments:
Attachments to File form fields
Attachments in process instructions
Form field attachments
Task assignees are permitted to upload these files while the task is in progress.
Attachments to process instructions
The owners of the process workflow are permitted to upload these files while editing the process.
The file can only be downloaded by participants who are not owners when the process workflow is in progress.