I currently only have the one label on the StatusStrip and all the properties are default.

Just in case something had become corrupt I deleted the label and added a new one but still got the same results

So I deleted the StatusStrip and added a new one populated with the same label and.......... it works fine.

The only thing I could think of is I had the original StatusStrip docked inside a ToolStripContainer, it's now docked within the form itself.

So I added a new status strip with a label to the ToolStripContainer and when I accessed the text property from the doWork event the exception was thrown.