How to use the CRL in ssl connection

[ben]

Hello everyone, 
  
I have a question about the crl in ssl server, I load the crl's file successed, 
but when one new connection come in, SSL_accept  return NULL, whether the 
client cert is in crl's file.l certainly if I didn't load crl file, the ssl 
server is very ok. 

 and the ssl_accept return the error msg: 
error:140890B2:SSL routines:SSL3_GET_CLIENT_CERTIFICATE:no certificate returned 

  
the code: 
int ret = SSL_CTX_load_verify_locations(ap_ctx, a_revokeCrl.c_str(), NULL); 
if ( ret == 0 ) 
{ 
    printf("SSL_CTX_load_verify_locations(crl) return 0."); 
} 
else 
{ 
X509_STORE *pCaCertStore = SSL_CTX_get_cert_store(ap_ctx); 
        X509_STORE_set_flags(pCaCertStore, X509_V_FLAG_CRL_CHECK); 
} 

openssl version:OpenSSL 0.9.8k 

This question was puzzled me two days, please superman help me, thank u very 
much! 
best regards!