I installed a Microsoft update today, Microsoft .NET Framework 4.5.1 for Windows 7 x64-based Systems (KB2858725).  After a reboot and some other updates I ran into a problem with Quickbooks Enterprise v11 (we haven’t upgraded due to issues in 12 & 13).  I received an error message whose exact text I did not copy but it went something like Error: QuickBooks has a problem in reading this registration file: qbregistration.dat .

Basically, Quickbooks could not open because it had lost my registration information.  I was directed to some help files by a Quickbooks popup message.  I validated that the file was in the proper location and intact.  I went to http://www.microsoft.com/en-us/download/details.aspx?id=15697#filelist and downloaded, then installed msxml.msi .  Once this package was installed, the issue was resolved.

This help article was useful though I picked a specific part of one method to a resolution shortcut:
http://support.quickbooks.intuit.com/support/Articles/SLN41019

I did not need to re-create the qbregistration.dat file but here is a relevant article:
http://support.quickbooks.intuit.com/support/Articles/HOW12495