Totally bizarre, I have developed a similiar problem since reading this post yesterday!!!
I booted my laptop this morning, fired up VS.NET, ran a project, ran a report and up came a very similiar error message about the file being corrupt. Never had a problem in the past, I re-booted and tried again and it worked OK but then after awhile it happened with a different report! This has now become a pattern...
I am using the same code as Eric and I have Adobe Acrobat 6.0 Pro.
I am just worried now that this problem will transfer to the clients site when I install the reports!