'This patch will only update version 1.3 to version 1.5"

I'm trying to reinstall RTW and EB on my PC because I suddenly had a nostalgic urge to play EB again, and I'd quite like to try to EB for BI installer. However, every time I try to patch my clean install of BI with patch 1.6, I get the error message in the title. I'm running Vista 64 bit (I know, a bit of a nightmare for old games) and I've tried copying both the RTW folders into Program Files and Program Files (x86), both of which have no effect.

Does anyone have any ideas?

What version of BI do you have? Some versions of BI come already patched to v1.6...