Batch / Bulk Naming Of Cells?

What I would like to do is take all of the subcategory headings and name the cells they are in to reflect them.

e.g.
E2 has text "Diodes, Low Frequency"
I would like to rename the cell so
Diodes_Low_Frequency has text "Diodes, Low Frequency"

The code I'm using is as follows:

Code:
Dim rng As Range
For Each rng In Range(E2, AD2)
'Title of subcategory

[Code]....

For this code I'm getting the error "Method Range of object _Global failed"

If I change the code to the specific Sheet4.Range(E2.AD2) I get the error "Method Range of object _worksheet failed"

The actual code to alter the test string works fine, its the selecting the range and writing the cell names that I'm having trouble with.