Q^6.1 Fitter dies

With MaxII designs, it happens that Q6.1 reports at 81% of the Fitter :

Internal Error: Sub-system: FMAIN, File: /quartus/fitter/fmain/fmain_location_constraint.cpp, Line: 3024

m_soft_locked_constraint.check_constraint( other_constraint->m_soft_locked_constraint)

Stack Trace:

0xA5CD : FITCC_CLOCK_REGION_CHECKER::set_oterm_alias + 0x26D6 (FITTER_FITCC)

0xC2DB : FITCC_CLOCK_REGION_CHECKER::clear_usage_for_all_oterms_on_atom + 0xE28 (FITTER_FITCC)

0x18DDA : FITCC_DESIGN::are_atom_location_constraints_mergeable + 0x132 (FITTER_FITCC)

0x1579A : fygr_execute + 0x1655 (fitter_fygr)

0x16FE2 : fygr_execute + 0x2E9D (fitter_fygr)

0xC57E1 : FYGR_TEMPLATE_REGISTER_PACKING_OP::find_shared_input_lonely_register_matings + 0x206 (fitter_fygr)

End-trace

Quartus II Version 6.1 Build 201 11/27/2006 SJ Full Version

Intresting that MaxII freezes at 81% .... if it freezes.