I just received this error when attempting to run an SSIS package I had modified. I (mis!)interpreted the error as a failed lookup, and made all kinds of changes to the package in attempts to prove that in fact there were no failed lookups, and wondering why it hadn't redirected the errors like I had told it to.
There used to be something here about how this was caused by copy/pasting the lookup transforms, but that has nothing to do with it. I can reproduce this without the copy/pasting. It's because I have more than one lookup transform referencing the same table. Once I disabled memory caching for those lookups sharing the same data, the problem went away.
I really think this is a bug. That is NOT the error message that should be shown for that situation.