MaxLength property of a TextBox control does not work when the TextMode property is set to Multiline. Here is small work around using regualr expression validator..

<asp:TextBox ID="txtComment" runat="server" Width="466px" TextMode ="MultiLine" ></asp:TextBox> 
<asp:RegularExpressionValidator ID="RegularExpressionValidator2" runat="server" ControlToValidate="txtComment" 
ErrorMessage="Not more than 50 charcters" Display="Static" ValidationExpression='^[\s\S]{0,50}$'> 
</asp:RegularExpressionValidator> 

 The File Upload server control provided by ASP.NET allows users to upload one or more files to the server. By default, ASP.NET permits only files that are 4,096 KB (or 4 MB) or less to be uploaded to the Web server. To upload larger files, you must change the maxRequestLength parameter of the <httpRuntime> section in the Web.config file.

<system.web>
  <httpRuntime executionTimeout="240" maxRequestLength="20480" />
</system.web>  

 The value of maxrequestlength is in KB. In this case it's allowed up to 20 MB

Here is sample code for TextBox Validation to allow Numbers only.

[code:c#]

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In Code behind add this function to "onkeyup" event for TextBox

[code:c#]

TextBox1.Attributes.Add("onkeypress", "CheckTextBox(this)");

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