向动网7.1模拟发帖,返回错误页面,抓包分析无果,望指教

我用.net向动网论坛发新帖,总是提示"请输入您的用户名，请确认您输入的用户名长度是否符合论坛标准。",抓包看了一下,发现浏览器和程序发送的cookies还有内容都差不多,不知道哪里除了问题,请大家看看
程序发送的内容:
POST /SavePost.asp?Action=snew&boardid=46 HTTP/1.1
Accept: */*
Accept-Language: zh-cn
Referer: http://bbs.ahau.edu.cn/post.asp?action=new&boardid=46
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; InfoPath.2; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30)
Host: bbs.ahau.edu.cn
Cookie: upNum=0; Ewwwrootbbs=userid=17&usercookies=3&userhidden=2&password=3O263U7hgc314ixb&userclass=%B0%E6%D6%F7&username=Thinking&StatUserID=2107821364; EwwwrootbbsKill=kill=0; ASPSESSIONIDQCARDTCC=OOFLEEMDOGMAPIDCOMNGGKHK
Content-Length: 357
Expect: 100-continueupfilerename=&Body=ThinkingThinkingThinkingThinkingThinkingThinkingThinkingThinkingThinkingThinkingThinkingThinking&dvbbs=Ewwwrootbbs&star=1&page=1&TotalUseTable=dv_bbs1&username=Thinking&passwd=********&font=&topic=Thinking&topicximoo=0&Expression=face1.gif&autofix=1&GetPostType=&ToMoney=&Buy_Orders=-1&Buy_VIPType=0&Buy_UserList=&signflag=yes&emailflag=0
浏览器发送的内容:
POST /SavePost.asp?Action=snew&boardid=46 HTTP/1.1
Accept: */*
Referer: http://bbs.ahau.edu.cn/post.asp?action=new&boardid=46
Accept-Language: zh-cn
Content-Type: application/x-www-form-urlencoded
UA-CPU: x86
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; InfoPath.2; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30)
Proxy-Connection: Keep-Alive
Content-Length: 379
Host: bbs.ahau.edu.cn
Pragma: no-cache
Cookie: Ewwwrootbbs=UserID=17&usercookies=3&StatUserID=21051497687&password=s85z611654r5uRGK&userhidden=2&userclass=%B0%E6%D6%F7&username=Thinking; EwwwrootbbsKill=kill=0; ASPSESSIONIDQCARDTCC=APFLEEMDDLGKHKPMHDADCGNB; upNum=0; Dvbbs=upfilerename=&Body=testtesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttest&dvbbs=Ewwwrootbbs&star=1&page=1&TotalUseTable=dv_bbs1&username=Thinking&passwd=**********&font=&topic=test&topicximoo=0&Expression=face1.gif&autofix=1&GetPostType=&ToMoney=&Buy_Orders=-1&Buy_VIPType=0&Buy_UserList=&signflag=yes&emailflag=0