Sql Server - Sporadic Data Error - "Cannot Find Table 0"?

Having deployed a new build of an ASP.NET site in a production environment, I am logging dozens of data errors every second, almost always with the error "Cannot find table 0." We use datasets and frequently refer to Table[0], and while I understand the defensive coding practice of checking the dataset for tables before accessing Table[0], it's never been a problem in the past. A certain page will load fine one second, and then be missing one of its data-driven components the next. Just seeing if this rings a bell for anyone. More detail: I used a different build server this time, and while I imagine the compiler settings are the same on both, I have a hard time thinking that there's a switch that makes 50% of my database calls come back with no tables. I also switched the project to VS 2008, but then reverted all of those changes when I switched back to VS 2005. I notice that the built assembly has a new MyLibrary.XmlSerializers.dll, where it didn't used to, but I also can't imagine that that's causing all the trouble. (It also doesn't fall down on calls to MyLibrary, or at least no more than any other time.)

Updated to add: I've discovered that the troublesome build is a "Release" build, where the working build was compiled as "Debug". Could that explain it? Rolling back to the build before these changes fixed it. (Rebooting the SQL Server, the step we tried before that, did not.)

The trouble also seems to be load-based - this cruised through our integration and QA environments without a problem, and even our smoke test environment - the one that points to production data - is fine under light load. Does this have the distinguishing characteristics of anything you might have seen in the past?