I'm trying to rename multiple TIF files.  I loaded the old file  name sccbka001.TIF, for example, in the Description/Caption field.  I'm using the Description/Caption field only for convenience it doesn't matter for the end result. I changed the "sccbka" to "StvCoCommMin" without problems.  Then I selected all, Rename files, entered  {captionwriter} in the rename block.  The sample front and back file names look good.  I just don't get an option to click on OK.  If I only do one file it works without problem.  There are six folders with about 3000 files total so I don't want to do this manually. 
I just upgraded to build 18327.  I'm using a Windows 10 Home laptop. 
Thanks for the help.