a bimolecular reaction

Hi, I am experimenting a TI perturbation with Amber 8.0 on an
 enzyme-catalyzed bimolecular reaction (an alcohol reacts with a
 carboxylic acid to form an ester).  The two species are away from each
 other in the enzyme pocket. First I run the simulation in vaccum
 without enzyme. I defined two new atom types for the carbonyl carbon
 (CX) and the hydroxyl oxygen (OX).  They will become C and OS at the
 end (in the ester) and one OH and two HO atoms will disappear.
 Initially CX and OX distance is 6.0 angstrom. When I run minimization
 on the unperturbed system, the 1-4 EEL blows up quickly. I suspect
 that this has something to do with the restraints between two
 molecules. I tried to play around the force constants and so far has
 no luck. Any suggestions will be welcomed.
 Eric
 Initial minimisation of our complex
  &cntrl
   imin=1, maxcyc=2500, ncyc=1000,
   cut=1000,ntb=0, ntpr=50
 /
 ...
    NSTEP       ENERGY          RMS            GMAX         NAME    NUMBER
     100      -8.6624E+01     6.0486E+00     3.0066E+01     C4          4
   BOND    =        2.9020  ANGLE   =       40.9876  DIHED      =       28.3713
   VDWAALS =       -3.3408  EEL     =       58.0670  HBOND      =        0.0000
   1-4 VDW =       12.8320  1-4 EEL =     -226.4433  RESTRAINT  =        0.0000
    NSTEP       ENERGY          RMS            GMAX         NAME    NUMBER
     150      -5.6925E+03     6.0827E+04     4.8485E+05     H15        15
   BOND    =        6.7995  ANGLE   =       78.2618  DIHED      =       38.3658
   VDWAALS =       -2.9570  EEL     =       54.6162  HBOND      =        0.0000
   1-4 VDW =       12.2254  1-4 EEL =    -5879.7886  RESTRAINT  =        0.0000
    NSTEP       ENERGY          RMS            GMAX         NAME    NUMBER
     200      -1.1864E+07     2.6376E+11     2.1022E+12     H15        15
   BOND    =        6.6603  ANGLE   =       78.2334  DIHED      =       38.3939
   VDWAALS =       -2.9575  EEL     =       54.6011  HBOND      =        0.0000
   1-4 VDW =       12.2257  1-4 EEL = *************  RESTRAINT  =        0.0000
 emark goes here
 MASS
 CX  12.010        0.616               same as c
 OX  16.000        0.434               same as o
 BOND
 CX-OX     10.0    6.0       weak restraint
 ANGLE
 CX-OX-CT  10.0  117.18
 CX-OX-HO  10.0  117.18
 O -CX-OH  10.0  120.00    same as O -C -OH
 O -CX-OX  10.0  120.00    same as O -C -OH
 OH-CX-OX  10.0  117.18
 CA-CX-OX  10.0  120.00    same as CA-C -OH
 DIHE
 X -CA-CX-X      4   14.50        180.0             2.  same as X -C -C -X
 X -CT-OX-X      3    0.50          0.0               3.  same as X -CT-OH-X
 X -CX-OH-X      2    4.60        180.0             2.  same as X -C -OH-X
 X -CX-OX-X      2    4.60        180.0             2.  same as X -C -OH-X
 IMPROPER
 NONBON
   CX          1.9080  0.0860             same as c
   OX          1.6612  0.2100             same as o