You will need to add a MicrosoftExcel component to you solution, it is found under Pega Robotics Connectors in the toolbox. Set the properties to open you excel file. Then you can read the value from B1 and place in the Path of the adapter, assuming this is a windows adapter.
i tried to replicate your error using the same automation steps as in Image3 but I can't get the error. Can you post an image of the properties for you microsoftExcel1 component and an image of your excel worksheet that includes the sheet names at the bottom.
OK, I was able to reproduce your issue. The problem is that when the Excel workbook is closed it cases the microsoftExcel1 component to Stop. Just add a Start call to the microsoftExcel1 component before your Open call.