I've been viewing the 1881 UK census CDs on this Windows 7 computer for two years without a hitch. Now suddenly, for no apparent reason, I can't view the data CDs, the error message is

Run-Time error 339
component 'FolioObjects.ocx' or one of its dependencies
is not correctly regstered: a file is missing or invalid.

Unfortunately I haven't used the CDs for a several weeks, and I can't get System Restore to go back further than a more recent Windows Critical Update. I have uninstalled the Viewer, installed again in Windows XP compatibility mode (as I did originally). The LDS site has a help page indicating it's a virus problem - but AVira AV and TrojanRemover say my system is clean.

Short of re-installing Windows 7, I can't think of anything else - I'd be grateful for help or advice.

Mary Young