If you have windows XP SP2 perhaps this might help: MS & 3rd party patches

Try deleting your Gnucleus preferences & see if that makes a difference to it opening.

Tried installing the MS-kb884020 patch but nothing.You said, try deleting the preferences, but i've left everything default this time (new install x4). So am unsure exactly what u mean.Gnucleus (2020) worked perfectly for me with all the updates until recently on the original install.Strangely when i made a new install of the same version it would'nt work,so I resurrected my my old install thru the magic of SATA,& it worked perfectly.Inevitably a different problem occurred & I lost that 2020 version.
With this many posts with the same problem,I think something smells in the state of ....,&maybe it's got something to do with Norton or more likely Microsoft.