One of the common causes of this problem actually has a fairly simple fix!
At Network or Good we maintain our contact records through the Guidstar.org non-profit database.
GuideStar automatically creates a Nonprofit Profile for 501(c) organizations registered with the IRS. When new profiles are created, all organizations are automatically opted-in for third-party donations. However, if your organization has been opted-out, please follow the link below for a walkthrough on how to opt your organization back in: