change the toolStripStatusLabel text fromfunction of class

Anyone knows how can I change the toolStripStatusLabel text which is in the main form, from the function of one class_
Means that when this function in the class is invoked and run into catch, inside catch there should change the text of the toolStripStatusLabel.
Any idea how to do that _ thanks a lot!public void AA()

{

try

{

}

catch

{

this.toolstripstatuslabel4.Text = "xxx";//wanted text }

}

But I can not do like this because it says> the name does not exist in the current context...
Any idea how to do that _ thanks a lot!