MAX.RES. is small but DELTEX keeps decreasing

Hi All,

I am running TOUGH3 EOS7C. The simulation seems stuck at extremely small time step. Please see below for the failure message. You can see that the residual is already very small but the time step keeps decreasing. Any idea what is causing this? 

Thanks,

Haiyan

 QQQQQQ SUBROUTINE QU QQQQQQQQQQQQQQ --- [KCYC,ITER] = [ 335,  1]
 ...ITERATING... AT [  335, 1] --- DELTEX = 0.966338E-09  MAX. RES. = 0.962728E-16 AT ELEMENT L2012  EQUATION   5
 TOUGH STATUS: Failed in EOS. IGOOD=           2
 +++++++ REDUCE TIME STEP AT (  335, 1) ++++++++++   NEW DELT =0.241585E-09