Berkeley DB Family

please help me find the reason of the following problem:
Condition: Berkeley DB 4.6.18;VxWorks 5.5; pentium BSP
my code is :

#include "db.h"
#include <stdio.h>
int db_main(void)
{
int ret;
DB *dbp;
u_int32_t flags;
if ((ret = db_create(&dbp, NULL, 0)) != 0)
{
fprintf(stderr, "db_create: %s\n", db_strerror(ret));
return 1;
}
if ((ret = dbp->set_pagesize(dbp, 1024)) != 0)
{
dbp->err(dbp, ret, "set_pagesize");
return 1;
}
if ((ret = dbp->set_cachesize(dbp, 0, 32 * 1024, 0)) != 0)
{
dbp->err(dbp, ret, "set_cachesize");
return 1;
}
flags = DB_CREATE;
ret = dbp->open(dbp, NULL, "BD/single.db", NULL, DB_BTREE, flags, 0);
if (ret==0)
printf("Opening DB is successful!\n");
else
{
dbp->err(dbp, ret, "%s open", "BD/single.db");
return 0;
}
dbp->close(dbp, 0);
return 0;
}

The error information on the target PC screen is:

stat: BD/_ _db.single.db: errno = 0x880226
BD/single.db: errno = 0x880226
BD/single.db open: errno = 0x880226

The information on the VxWorks's WFTPD is following:
Command"CWD BD" reveived
CWD D:\BD successful
Command "PASV" received
Command "RETR single.db" received
RETR failed -file does not exist
RETR failed -file does not exist
Transfer aborted
......
Command "STOR _db.single.db" received
STORe started on fiel _db.single.db
Transfer finished
......
Command "RETR_db.single.db" received
RETRieve started on file _db.single.db
Transfer finished
Got file D:\BD\_db.single.db successfully
Command "QUIT" received

This problem I asked some days before.
And I give the whole information I can get this time.
Please help me on this question, I have spent two weeks time on it.

Thanks a million.