Can’t open 2 folders at once on desktop

Fixed this up for a retired neighbor: old Compaq 200 MHz MMX 96Mb RAM, with W98 SE, MS O2k, Ontrack Fix-It 3.0 (he had this and wanted it in, against my better judgement). All finished, everything seemed to work fine . . . until I tried to open two folders on the desktop at the same time (to compare contents). Will not happen!
I’ve tried all I know, including most of a day comparing the registry with another on a similar setup, and removing apps one at a time. He can get by, but the problem annoys the hell out of me!