I had an error of this type just yesterday.

Weird as it may sound the problem went away when I opened the Project, replaced a UserControl's toolbox bitmap (with the same image as originally used), and recompiled.

Weird, but I suspect that the .CTX file had been corrupted somehow.


Previous to the problem I was getting weird "file I/O error" dialogs when I compiled and saved. Still no idea what I was doing wrong, but after a reboot I had reopened the Project, compiled, and then the compiled EXE got those "Your version may be outdated" pointing an accusing finger at my UserControl.

Again, replacing the toolbox bitmap and recompiling solved it.