I am loosing drawing DWG or IDW thumbnails which show up as black squares instead when looking in the library, and this 'Black Thumbnail' issue is repeated when printing a drawing which appears fine on screen but the rendered ISO view prints as a black square, you can see in the printed black square the image it was supposed to print?In the 'Designs' library the folders are mostly displayed correctly with 4 thumbs in each but some have the thumbnail as black squares? These files open correctly even though the they show as a black square?All the IPT and IAM files display correctly?
 
The files are kept on a server and I can open & edit if required but they show as black?
I am using Inventor 2008 with Windows XP Pro 5.1.60 service pack 3 with 4GB ram ATI radeon X550 128MB.
I can email a screen shot if required.
Many thanks in advance for help in this matter

This Problem is now rectified by upgrading my graphics card to Nvidia Quadra FX580 which although now classed as entry level has removed the problem. corrupted files are corrected by opening and adjusting a dimension saving and then amending back to its original parameter and saving once more.
Thanks also to Kevin at Quadra Solutions for all your help.