Symptoms

Customer is using the SharePoint Documents SmartObject to upload a file to a SharePoint document library. Customer requirement is to allow a user to upload a new version of an existing document, and track the versions. The SmartObject call was throwing an error when executing.
"Server was unable to process request. ---> File Upload failed - File already exists."
 

Diagnoses

Support reproduced the error when using the "Create" method. This is likely because the "Create" method is intended to only handle the situation of creating a new file.
 

Resolution

Use the "Update Document" method, rather than the "Create" method.
Using the "Update Document" method will upload the file, if it does not already exist. If the file already exists, and versioning is enabled in the SharePoint document library, a new version of the file will be created.