Vista - Windows Photo Gallery - Tags Missing

I am using Vista Home Premium.

A lot of my .jpg photo files have lost their Tags.

When I open Windows Photo Gallery the Tag names still appear in the left
pane but when I click on the Tag name there are no photos shown.

When I click on the Not Tagged heading the photos that have lost their tags
do not appear.

When I go to START>PICTURES all of my photos are displayed, including the
photos that have lost their tags. If I then select a photo and try to
change the tag in the details at the bottom of the screen and click SAVE, I
get this error message in a Dialog Box headed "Apply Properties File"

An unexpected error is preventing the operation......................Error
0x88982F50: No error description available

It offers a Retry or Cancel button, but retry just gets the same error.

I am also unable to use Windows Photo Gallery for editing other .jpg file
properties.

There are plenty of comments revealed by a Google search, but they do not
seem to lead anywhere.

Can anyone help me with this please.

Ian