Q: 10.10.3 upgrade has Time Machine stuck in Preparing Update

Since I upgraded my Macbook Pro to 10.10.13 my Time Machine is showing Preparing backup endlessly.  The last backup was immediately before I installed the update.  How do I get Time Machine to complete a backup of system with the new update applied?  I have a MacBook Pro 13 in, Late 2011 with a 2.4 GHz Intel Core i5 processor and 4 gb memory.  I have tried turning time machine off and on and rebooting with the Time Machine attached.