When opening a document from a library within SharePoint (which requires check out), you are prompted if you want to use your local drafts folder for the checked out file. If you tick the box to use your local folder the document is copied to your local SharePoint drafts folder which is normally C:\Users\<username>\Documents\SharePoint Drafts\. Its then copied back when you check in.
This is fine; however I have experienced random issues if the local drafts folder is pointing to a remote server. Ie \\<servername>\<share>\<username>\Documents\SharePoint Drafts\. The main issue was Word refusing to publish the document as a major version. You select major, type in your comments, but it only adds the document as a minor! This then fails to start the workflow.
A quick and easy fix:
You can change the client application to use the SharePoint server for the drafts folder. To do this load Word Options, Click Save options, then select Save Checked Out Files to: The web server.
Alternatively you can edit the following registry key value. Useful if you have a lot of machines to update.
Another key which is worth a mention is:
This will disable the initial check out dialog you see when launching the document from SharePoint.