Working With Muliple Workbooks/xls Files

in simple terms im trying to cross reference a name list with registers from another wrokbook. so basically the desired result is. i press my button and it loads the second workbook up, it then uses the a name list in the new book and searches for that names maches in the registers (a group of sheets) on the previous workbook then if a match is found it colours the background in green. I am however getting errors e.g. "run time error: '424': Object required"

with this line then highlighted in yellow:
u = ShtNm.Sheets("Sheet1").Cells(1, "C").Value

Sub Macro1()
Dim u As Integer
Workbooks.Open FileName:= _
"S:HR TrainingO2 Operational TrainingRetentions and CollectionsUpgrades
ames 18th june onwards.xls"
ShtNm = ActiveWorkbook.Name...............