System.FormatException occurs when attempting to convert a numeric string to a numeric data type

Source: Microsoft Support

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You attempt to cast a numeric string to a numeric data type, using code similar to the following.

Dim strInput As String = "10"
Dim intResult As Integer = 0
Try
intResult = Convert.ToInt16(strInput)
Catch ex As Exception
MessageBox.Show("Error: " & ex.Message)
End Try

You receive a System.FormatException with the following error and stack trace.

"Input string was not in a correct format."

A first chance exception of type 'System.FormatException' occurred in mscorlib.dll
at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal)
at System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info)
at System.Int16.Parse(String s, NumberStyles style, NumberFormatInfo info)
at System.Convert.ToInt16(String value)
at TypeConversionTest.Form1.cmdConvert_Click(Object sender, EventArgs e) in C:\Source\TypeConversionTest\TypeConversionTest\Form1.vb:line 7

There is an incorrect value in the following value in the Windows registry:

HKEY_CURRENT_USER\Control Panel\International\sPositiveSign

This value should be empty for most English Language settings. Note that when this error occurs, the value may appear empty visually, but may contain a space or unprintable character.

While it is possible to directly edit the value for the problem key, the preferred method is to change the Regional Settings to a different Region/Language and then reset it to the desired setting:

1. Open the Regional and Language Options applet from the Control Panel.
2. Note the Current Format.
3. Change the Current Format to English (Australian)
4. Click Apply.
5. Change the Current Format to the noted format, eg, English (American).
6. Click Apply and then click OK.

This action resets every value under the HKEY_CURRENT_USER\Control Panel\International registry key.

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