Terrible, so I took out the files from the Effect Folder then I ended up with black squared smoke on touchdown.

Did a search in the hope of finding a cure and came up with this from Flightsim:
gauges_recovery_fsx.zip
Not only does it re-install all default FSX effects it also re-installs all the default gauges as well, you can choose which installs you want so now I have my white smoke effect back and working.
Nice handy tool to have.
Regards
Nigel.