Workflow Error

Hi, 

I have a workflow in place that is throwing up the following error - 'workItem is null'

I've tried a lot of different variations on the formulas and am still getting this - but only when I create a new project with a parent. I only want this to run on leaf projects and tasks, which it is doing fine when I move or edit a leaf item and doesn't run when I create a new project without a parent. I have the following evaluation in place

Not(IsNull($Parent))&&(IsLeaf($Project))

and the actions are as follows

IF((Contains($Parent.Name,'Target',False)),'Target',IF((Contains($Parent.Name,'Pending',False)),'Pending',IF((Contains($Parent.Name,'Good Prospect',False)),'Good Prospect',IF((Contains($Parent.Name,'Awarded',False)),'Awarded',IF((Contains($Parent.Name,'Complete',False)),'Complete',IF((Contains($Parent.Name,'In Progress (Construction)',False)),'In Progress (Construction)',IF((Contains($Parent.Name,'In Progress (Prelims)',False)),'In Progress (Prelims)',IF((Contains($Parent.Name,'Archiv',False)),'Hide - Completed','Hide - Completed'))))))))

IF((Contains($Parent.Name,'Target',False)),'Light Grey',IF((Contains($Parent.Name,'Pending',False)),'Light Grey',IF((Contains($Parent.Name,'Good Prospect',False)),'Light Grey',IF((Contains($Parent.Name,'Complete',False)),'Light Grey',IF((Contains($Parent.Name,'Archiv',False)),'None','None')))))

IF($Parent.C_SBU='BSERV','BSERV',IF($Parent.C_SBU='ECDC','ECDC',IF($Parent.C_SBU='FP','FP',IF($Parent.C_SBU='HDC','HDC',IF($Parent.C_SBU='Healthcare','Healthcare',IF($Parent.C_SBU='LS / SC','LS / SC',IF($Parent.C_SBU='POL','POL',IF($Parent.C_SBU='Archived','Archived','Archived'))))))))

Any advice?