How I will know, the forum that use in what version?

Cause, my forum it can't attach file such as PDF, doc, xls etc. I should do it???

Please help me

Thank, I use forum in version 3.20.01, In this version I can select in check box for this forum can attach file or not attach file but I can not attach file.

When I click button 'Browse' for select file to attach and then I click 'add' for add in this attach file to server but show 

Server Error in '/' Application.

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Value cannot be null. Parameter name: format

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.ArgumentNullException: Value cannot be null. Parameter name: format
Source Error:

Stack Trace:

[ArgumentNullException: Value cannot be null.
Parameter name: format]
   System.String.Format(IFormatProvider provider, String format, Object[] args) +133
   DotNetNuke.Modules.Forum.AttachmentFile.ValidationInfo(Config ForumConfig) +600
   DotNetNuke.Modules.Forum.AttachmentPage.AddFile() +109
   DotNetNuke.Modules.Forum.AttachmentPage.cmdAdd_Click(Object sender, EventArgs e) +61
   System.Web.UI.WebControls.LinkButton.OnClick(EventArgs e) +108
   System.Web.UI.WebControls.LinkButton.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +57
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +18
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +138
   System.Web.UI.Page.ProcessRequestMain() +1277

Version Information: Microsoft .NET Framework Version:1.1.4322.573; ASP.NET Version:1.1.4322.573

Pls, help me...