opening microsoft excel files in numbers

I received these document warnings when I opened my Numbers '09 version 2.3 file:

Missing File - pct256.tiff

Missing File - pct259.tiff

Missing File - pct202.tiff

Missing File - thumbs/proto-thumbail-Sums Checklist.tiff

Missing File - pct508.tiff

Missing File - pct2510.tiff

Missing File - pct504.tiff

Missing File - thumbs/proto-thumbail-Basic.tiff

Missing File - thumbs/proto-thumbail-Sums.tiff

Missing File - thumbs/proto-thumbail-Plain.tiff

Missing File - pct505.tiff

Missing File - pct507.tiff

Missing File - pct503.tiff

Missing File - pct203.tiff

Missing File - thumbs/proto-thumbail-Headers.tiff

Missing File - thumbs/proto-thumbail-Checklist.tiff

Missing File - pct506.tiff

Missing File - pct257.tiff

Missing File - pct258.tiff

This file was imported from Microsoft Excel 2008 for Mac Version 12.3.6.

Anyone know how I can get rid of the warnings and what they mean?