输入字符串的格式不正确的问题
在窗体上有一个文本框，希望通过输入的数字，比如1000作为条件来进行查询，并将结果显示在datagridview1上。代码如下，但是总是提示：


未处理的“System.FormatException”类型的异常出现在 mscorlib.dll 中。

其他信息: 输入字符串的格式不正确。


究竟什么问题啊！？疯了！
Imports System.Drawing
Imports System.ComponentModel
Imports System.Windows.Forms
Imports System.Data.OleDb
Imports System.Data
Imports System
Public Class Form4

Private Sub Form4_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
'Me.Parent = Form1

End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim myConn1 As String = " Provider = Microsoft.Jet.OLEDB.4.0 ; Data Source = hyjf.mdb"
Dim myConn As OleDbConnection = New OleDbConnection(myConn1)
myConn.Open()

Dim fee5 As String = TextBox1.Text
Dim fee4 As Single = Convert.ToSingle("fee5")//这句报错！！！！为什么呢？！
Dim str2 As String = " select * from members where fee>fee4 "

Dim cmd2 As OleDbCommand = New OleDbCommand(str2, myConn)
Dim mydata As OleDbDataAdapter = New OleDbDataAdapter
Dim ds As DataSet = New DataSet
cmd2.ExecuteNonQuery()
mydata.Fill(ds, "members")
DataGridView1.DataSource = ds
DataGridView1.DataMember = "members"
End Sub

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
Me.Close()
End Sub
End Class


[解决办法]
问题已解决。