Server version: 188.8.131.52
Viewer version: 184.108.40.206
In UltraVNC Edit Settings, the Input/File Transfer tab, these are both checked:
User Impersonation (for Service Only)
OS version: Windows XP SP3, 32-bit, both server computer and viewer computer.
No problems viewing or using File Transfer on other computers on the same network, with the same settings. The others are using Server version 220.127.116.11.