Column number reference using cell reference

Hi all,

I have created a basic macro which hides columns before and after a specified range. I have calculated the column numbers from a user specified date in excel and want to use these cell references in my VBA code to hide the columns.

For example:

Cell B9's formular tells me the users date starts at column 37.
Cell B10's formular tells me the users date ends at column 42.

Becuase these dates change I need to reference cells B9 and B10 and not the column numbers 37 and 42.

So I want to hide colomns 4:B9 and B10:55.

My code keeps failing with error "type mismatch".

Sub Hide_ProjectA()
'
' Hide_ProjectA Macro
' Hides columns outside a specified project date range

'Unhide all columns
Columns("D:BC").Hidden = False  'Unhide all week Columns

'Hides all columns before project A
ActiveSheet.Columns("4:B9").EntireColumn.Hidden = True

'Hides all columns after project A
Columns("B10:55").Hidden = True


Application.ScreenUpdating = True


End Sub

Any help would be great!