Just a quick tip for anyone designing an InfoPath-based solution that uses the built-in file attachment control. We’ve recently built an application that uses browser-based InfoPath forms, a set of SharePoint designer workflows, and a series of custom lists and libraries. Everything works beautifully until the size of the attached files starts to get over a few megabytes. While there are settings in Central Admin that allow you to boost up the size of form submissions, we’re finding both instability and a tendency for the workflows to fire before the form finishes uploading – generally resulting in failures and a bad user experience. So a quick tip to make sure you thoroughly test attachments in your environment if you’re going to use this control, and make sure you know where the “breaking point” is for your infrastructure.

Update: after spending a few days off and on with Microsoft’s Premier Support it sounds like this is a known issue between InfoPath and SharePoint. Unfortunately they didn’t have much to offer other than some code samples to build a workaround in .Net. One trick that we developed was to add short pauses to the workflows, which does help ensure the workflow actions don’t fire prematurely. If your application requirements allow it, you may want to stay away from the file attachment control and simply have your users put documents into libraries and then include a link in the InfoPath form.