External Display not Working in Seamless Mode

When I connect the two PCs using Multiplicity, the mouse and keyboard sharing works fine. However, whenever I try to enter seamless display mode, the screen on my secondary device goes black. The strange thing is my cursor still appears on the secondary display, but the I cannot see anything else or drag windows into the display (the window disappears but the cursor remains visible). Additionally, the display borders seem to be offset, as I can drag the mouse off the screen to one side, but cannot even reach the edge of the screen on the other.