Gaussian: Error on Z-matrix card number

Dear CCLers,
 If I run relaxed Potential Energy Surface (PES) scan under Gaussian 98, the
 Z-Matrix card error always comes to me.
  Error on Z-matrix card number   11
  angle Alpha is outside the valid range of 0 to 180.
  Conversion from Z-matrix to cartesian coordinates failed:
 I explored on this issue. There are two possible situations related to this.
 One is the Z-Matrix definition on ring system. The other is the torsional
 angle reaching 0 degree. (Please let me know if I am wrong.)
 Did anyone meet these problem before? Could you please give me a suggestion?
 I will summary the result.
 Thank you and have a good day,
 William Wei
 Molecular Design and Information Technology (MDIT) center
 Faculty of Pharmacy, University of Toronto
 19 Russell Street, Toronto, ON. M5S 2S2
 Tel: 1-416-946-8469
 Fax: 1-416-978-8511