Shared Haptic Virtual Environments (SHVEs) are often realized using a client-server architecture. At the server, a physics simulation engine calculates the object states based on the position information received from the clients. At the clients, the object state information, received from the server, is used to update the local copy of the virtual environment. Forces displayed to the user through a haptic device are computed locally at the client based on the interactions with the objects. Communication delay leads to delayed object state updates and increased interaction forces rendered at the clients. Users perceive this as increased object weight. In this paper, we systematically analyze the loss of transparency caused by communication delay and propose a novel adaptive force rendering scheme to compensate for it. The proposed scheme reduces the objects' stiffness at the clients, based on delay, device velocity and motion constraints of the objects, only if necessary to achieve perceptual transparency. Simulations and subjective evaluations show that the effect of increased weight of objects is successfully compensated for the tested delay range of up to 150 ms. At the same time, if the object is unmovable, the perception of interaction with a rigid object is preserved.