修改密码出现错误，如何解决？

[itfuture01]

做了个mis系统，我想实现如下目的：用户登陆以后，可以修改密码，修改密码时要先输入旧密码，才能设定新密码。具体代码如下：
Private Sub cmdOK_Click()
Dim txtSql As String
Dim mrc As ADODB.Recordset
Dim MsgString As String



If Trim(txtoldpwd.Text) = "" Then
MsgBox "请输入旧密码", vbOKCancel + vbExclamation, "警告"
txtoldpwd.SetFocus
txtoldpwd.Text = ""
Else

txtSql = "select * from user_info where user_id='" & username & "'"
Set mrc = ExcuteSQL(txtSql, MsgString)


If mrc.Fields(1) <> txtoldpwd.Text Then
MsgBox "密码错误，重新输入", vbOKCancel + vbExclamation, "警告"
txtoldpwd.SetFocus
txtoldpwd.Text = ""
Else
mrc.Fields(1) = txtnewpwd.Text
mrc.Update
mrc.Close
MsgBox "密码修改成功！", vbOKCancel + vbExclamation, "密码修改"
Unload Me
End If
End If
End Sub

运行时出现以下错误：
BOF或EOF中有一个是“真”，或者当前的记录已被删除，所需的操作要求一个当前记录。
我认为是username=""的问题，应该获取当前用户名？但是如何获取呢？
如果不是这个问题，是哪里的错误？请指教！

[MSSQL]

Private Sub cmdOK_Click()
Dim txtSql As String
Dim mrc As ADODB.Recordset
Dim MsgString As String



If Trim(txtoldpwd.Text) = "" Then
MsgBox "请输入旧密码", vbOKCancel + vbExclamation, "警告"
txtoldpwd.SetFocus
txtoldpwd.Text = ""
Else

txtSql = "select * from user_info where user_id='" & username & "'"
Set mrc = ExcuteSQL(txtSql, MsgString)

if mrc.eof then
mrc.close
exit sub
end if

If mrc.Fields(1) <> txtoldpwd.Text Then
MsgBox "密码错误，重新输入", vbOKCancel + vbExclamation, "警告"
txtoldpwd.SetFocus
txtoldpwd.Text = ""
Else
mrc.Fields(1) = txtnewpwd.Text
mrc.Update
mrc.Close
MsgBox "密码修改成功！", vbOKCancel + vbExclamation, "密码修改"
Unload Me
End If
End If
End Sub