if it is winXP... try the fix for secure sites... at a dos prompt or run dialogue:
regsvr32 softpub.dll
regsvr32 wintrust.dll
regsvr32 initpki.dll
regsvr32 dssenh.dll
regsvr32 rsaenh.dll
regsvr32 gpkcsp.dll
regsvr32 sccbase.dll
regsvr32 slbcsp.dll
regsvr32 cryptdlg.dll
press return after each and it should confirm as succeeded. I have used this loads of times for people and it always works.
For the full m$ article see knowledge base number
813444
MB