John,
We updated from 4.0 to 4.5 back in May and had no issues in terms of the connection.
We did, though, apply an Add-In patch when it was released back in April time period ... perhaps check that bit as well. I believe that patch may have been included in an OSS note if not directly on the download site.
Regards,
Clay
PS ... I went ahead and looked up the OSS note that has the patch from April 2015 --
2150292 - Demand planning add-in for Excel Patch 1 based on EPM 10
SP20 Patch 1