[3.0/LINQ] Window1 dosnt contain a definition for 'Invoke'

[Rattlerr]

Here is the line of code with the Invoke in it::

this.Invoke(new delUpdateHistory((this.UpdateHistory)), para);

The Line Below is the Delegate for the above::

public delegate void delUpdateHistory(string str);

Which goes to this section of code::

public void UpdateHistory(string str)
 
{
 
// some code
 
}

this.Invoke produces this error::

Error 1 'iSCS.Window1' does not contain a definition for 'Invoke'

Invoke from what i have read is supported by .NET 3.0 Framework so the above code should work,unless i'm missing something.The code works fine in .NET 2.0 so, i'm not sure what is wrong here

So how do i go about fixing this??