residue type undefined

["J.U. Flanagan Biomedical Research Centre" <>]

Hi all,

Could anyone tell me what this error message is indicative of, and how I 
can fix it? 

iup2crm_E> IUPAC atom not found in topology library: CG
iup2crm_E> residue type undefined
recover__> MODELLER_STATUS >=  STOP_ON_ERROR:   1  1

Thanks in advance

Jack