Thanks , Marg7. Did all that but still got problems: deleted Sygate, downloaded fresh copy from Tucows. Got as far as "Removing backup files" in the installation and up comes "SMC has caused an error……"etc, etc. Click on that to close it, and Sygate installation seems to leap to "Completed" ( or a similar expression).
No icon appears for it on the desktop, and it's not listed in All Programs. Delete and start again - and so on several times, inc Start>Search for files named Sygate.
Eventually I also searched for Files named SMC.EXE , found them and deleted them. Then start all over again downloading fresh copy of sygate – this time from Simtel site as tucows seemed to have problems ("cannot open page" even while the files were apparently being downloaded from the site). Started to install the files downloaded from simtel and guess what – "Smc has caused an error….etc" at exactly the same stage as before.
During the afternoon I've also run another scan with A-squared which found and deleted Heuristic,Archive bomb - symptoms of which sound very like what I've been experiencing. Apart from that all seems clean; but I can't install Sygate.
I'm at my wits end. Can anyone solve this for me, PLEASE.