I am experiencing problems with sage pay iframe integration but only when using IE 10 running in Metro mode under Windows 8.
Running the same web site using IE 10 Windows 8 desktop mode runs fine.
The error that I am seeing is:
Error from Sage Pay: 5004 : The Transaction state is invalid.
As a precautionary measure I turned off "Enable Protected Mode" in IE but this did not stop the error occurring.
I got to the bottom of this issue.
It was caused by custom mark-up that is applied via the MySage control panel.