getting rid of a white box around an object

Hi. Please help!

I am a beginner and have used correldraw essentials to draft a diagram.  the diagram consists of several layers, all of which are drawn from scratch and some of which overlap. 

In previous draft versions, there has been no issue, but recently there is this annoying rectangular box (usually white, enveloping the object in question).

Can somebody please help me with instructions to remove it?

 

Grateful thanks!