This means the asset is missing textures. Look in the asset's folder to see if they are in fact there.
Open the Asset for editing in Explorer.
Look for the textures. If they are not there, remove the .text.txt file that relates to them.
close the Explorer window, and recommit the asset.
The error should go away then.
If the files are in fact there, run tools from PEV soft. (search fo PEV Soft Tools).
John