Spartan: MM2 parameters problems

 We have a student here using Sparatan to examine silarylene siloxanes.  He has
 no problem when carbon is substituted for the silicons.  However, when
 he includes the silicone atoms, he gets the following in the output file:
 SPARTAN MECHANICS (MM2) PROGRAM:  SGI/R4K  Release 4.1 a2
   (Job run on ucmodl.che.uc.edu)
 test
 Missing angle parameter: 2 19 6  0 (2 1 13)
 Not being familiar with Spartan, I cannot make any sense out of this error
 message.  I suspect that some valance bond angle parameter is missing for the
 silicon atom but which one?  Looking in the params.MM2 I do not see any
 indication of what atoms correspond to which set of parameters.
 Any suggestions will be helpful.  Thank you in advance.
 --
   Jeffrey L. Nauss, PhD           Telephone: 513-556-0148
   Dir. Molec. Model. Serv.        Fax:       513-556-9239
   Department of Chemistry         e-mail: Jeffrey.Nauss (- at -) UC.Edu
   University of Cincinnati        URL http://www.che.uc.edu/~nauss