Metadata warning -- and I don't know what to do? :(

Question

Hello, I recently moved my Lightroom from a pc to a mac.  Right after I started getting a pop up that says:
"the metadata for this photo has been changed by another application. Should lightroom import setting from disk or overwrite settings with those from the catalog?" 
There's also an upward facing arrow on image where this warning pops up. 
I have a screen shot I can show you but not sure how to upload that here.  I don't know what this warning means or what to do.  Can anyone help?  Reaching adobe CS is challenging to say the least. 
Thank you so much!

Answer 1

If you haven't changed develop settings or metadata "externally" (outside Lightroom), just choose 'Overwrite Settings', which means essentially "the develop settings and metadata in my catalog are to be kept, so quit bugging me..".
To solve all at once - select all photos and hit Cmd-S.
Detailed background info:
Lr is monitoring disk files and if ever they change (since photo changed in Lightroom), you'll get that message. Usually, they change because you edited them in another app, e.g. Ps/Bridge or manufacturer's software, in which case Lr is trying to warn you that catalog settings and disk files have both changed and so Lr has lost confidence in settings and metadata and you must dictate which are to be kept. Often Lr is smart enough to know there is no conflict, but not always (sometimes there are red-herrings/false-positives that throw it off..).
PS - ChangeManager (a free plugin I wrote) will list differences in develop settings and metadata in catalog vs. disk files, in case you want to see exactly what's different.
R