help: what's the meaning "dereferencing pointer to incomplete type"

["Xiaoshan Sun" <xssun@xxxxxxxxxxxxxxxx>]

hi,
  i have a programming problem using gcc compiler.
  when i compile a C source file ,i got the error message:
"dereferencing pointer to incomplete type"
this is caused by a line:
pqtemp->offset=0;
where "pqtemp " is a pointer of a "struct type".
so i need someone tell me what does the error message
"dereferencing pointer to incomplete type"
refer to ??

thanks .