Hi,
I had exactly the same problem with my FS7 foot switch. But I think I've just fixed the issue.
Apart from setting the EXP/FS to FS4 and FS5, I changed the 'TIP POLARITY' to 'Inverted' and the 'RING POLARITY' to 'Inverted'. They were both previously set to 'Normal'.
Just to clarify, this is in 'Global Setting' under 'Preferences'.
As far as the foot switch, it seems to work if the polarity is set to l or ll. And of course it's set to Momentary.
Now my FS7 is working fine.
Hope that helps!