Mysterious FormatException for Convert.ToInt32()...

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Cheers to all the mavens out there on codeproject!

I've banged my head over this one for some time, and I don't understand the reason for this FormatException (log entry) as thrown by Convert.ToInt32 that uses an input value from an ASP .NET 2.0 form *with* validation:

<br />ERROR 16 Jul 2009 09:01:13,970 (Webpage code-behind class name) - Failed conversion of value<br />System.FormatException: Input string was not in a correct format.<br />   at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal)<br />   at System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info)<br />   at (name of calling function in ASP.NET code-behind)<br />

The code-behind of the web page is as follows:

<br />try<br />{<br />    dataObject.Weight = Convert.ToInt32(txbWeight.Text);<br />}<br />catch (Exception e)<br />{<br />    log.Error("Failed conversion of value", e);<br />}<br />

And the web page has the following validation for the txbWeight TextBox control:

<br /><asp:CompareValidator runat="server" ControlToValidate="txbWeight" Type="Integer" <br />Operator="GreaterThanEqual" ValueToCompare="0" Text="Positive number only for weight."<br />Display="Dynamic" /><br />

I don't understand why this exception is thrown, because the validator ensures that an integer is being received from the user (txbWeight also has a RequiredFieldValidator). The odd thing is that dataObject receives the value despite the exception being thrown!? I don't believe I need to call Trim(), and trying this in the past did not fix the issue.

Any ideas?