Userform Listbox data from different workbooks

Please help, I have created an userform listbox in workbook A and RowSource points to a specific range of values in a particular sheet in workbook A. The macro is activated by CTL(z). This part works fine as long as the active workbook is A. I want to activate the listbox from a different active workbook say B. The List box appears but no data because the rowsource points to a range in workbook A. I have tried to put Workbooks("workbook A") in rowsource but still no success. Any suggestions would be appreciated.