Internal error with topology.c

Hi,

 When I try to run a Spectre dc and trans simulation with my 8-bit-adder circuit, have an internal error stopping the simulation.  I get the following messages in the spectre log window:

1) the usual "unable to compile ahdlcmi module library" message (which has not stopped my simulations in the past),

2) a warning from spectre during initial setup about having PMOS and NMOS from the driver circuit running at 1 A/exceeding imelt = 10 mA (the test driver/load circuit provided by our course instructor)

3) "Internal error found in spectre during topology check, during initial setup." --> "Assertion failed in file 'topology.c' at line 1008"

Any ideas how to interpret error #3??  I've done the Virtuoso save and check with no error for the 8-bit-adder or any of the lower schematics in the hierarchy.

To explain how I'm implementing an 8-bit-adder:  The design is four 2-bit-adders linked together.  Each 2-bit-adder is made of 2 individual adders.  Individual adders have Carry Out implemented with CMOS and Sum implemented with pass-logic transistor gates.

Thank you for your time.