System Error when using long equations?

Hi,

I was using MathCAD Express Prime and whenever I randomly get the system error called System Error: Item have already been added. Key in dictionary: System.Int32[] Key being added: System.Int32[]

It was working fine until recently. This error has been occuring in seemly random locations and times in vector locations such as FaccumTA(6)=

What should I do?

Thanks!