I m getting the error: Runtime error 91: “ Object variable or With block variable not set”

I was asked to design the work allotment process for the company. Work is allotted in the given manner: If suppose a task T1 is allotted to a person for 5 days, it should be displayed against his name for 5 consecutive days in the work allotment file. I have written a Visual basic code in MS Excel using macros in the third sheet - MAY of workallotment.xlsm and the tasks are in file tasks.xlsx . I m getting the error: Runtime error 91: “ Object variable or With block variable not set” while searching for the members name in workallotment.xlsm

I have also tried setting the findrow variable like "set FindRowNumber = rngFindValue.Row" But I get a compiler error saying object required .I attach both the files workallotmetn.xlsm and tasks.xlsx