opnet中仿真aloha出现错误，求帮忙

如题，求错误原因，是不是缺少什么文件了？
Errors reported by the binder program follow
(these messages have been saved in (C:\Users\will\op_admin\tmp\bind_err_4104):
正在创建库 C:\Users\will\op_models\cct_network.project\cct_network- aloha.dev32.i0.nt.lib ºÍ¶ÔÏó C:\Users\will\op_models\cct_network.project\cct_network- aloha.dev32.i0.nt.exp

aloha.dev32.i0.pr.obj : error LNK2001: 无法解析的外部符号 "int subm_pkts" (?subm_pkts@@3HA)


C:\Users\will\op_models\cct_network.project\cct_network- aloha.dev32.i0.nt.dll : fatal error LNK1120: 1 无法解析的外部命令


在Head block的代码为：
/* Input stream from generator module */
#define IN_STRM 0

/* Output stream to bus transmitter module */
#define OUT_STRM 0

/* Conditional macros */
#define PKT_ARVL (op_intrpt_type() == OPC_INTRPT_STRM)

/* Global Variable */
extern int subm_pkts;