ExcelBanter - Preventing user entering duplicate values in a cell range

I have a series of horizontal cells (7 IN ALL) that we use to track which
phases a document status is currently in.

A. not started=NS
B. in-progress=IP
C. under review=UR
D. reviewed=R
E. approved=A
F. on hold=OH
G. cancelled=C

We simply enter: "0"=NO or"1"=YES (Currently enter this manually and at
times fine that a document has to many "1"'s in a particluar row.

All phases will be populated with a "0" to begin with and the user will
enter/move "1" as the document progresses through each phase.

+---+-----+-----+-----+-----+-----+-----+-----+
| | A | B | C | D | E | F | G |
+---+-----+-----+-----+-----+-----+-----+-----+
| 1 | NS | IP | UR | R | A | OH | C |
+---+-----+-----+-----+-----+-----+-----+-----+
| 2 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
+---+-----+-----+-----+-----+-----+-----+-----+
| 3 | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
+---+-----+-----+-----+-----+-----+-----+-----+
| 4 | 0 | [1] | 0 | 0 | [1] | 0 | 0 | <<I want to avoid
double enteries
+---+-----+-----+-----+-----+-----+-----+-----+
The brackets are merely to highlight the duplicates

To avoid the user entering duplicates €œ1€ in a range of cells i.e. A4:G4. I
want to
incorporate a feature that will not allow the user to enter €œ1€ in multiple
cells in the ROW.

For example: if the user enters a €œ1€ in B4 (In-progress) and then returns
later to update the document phase and enters a €œ1€ in C4 (Under Review)
cells A4, B4, D4, E4, F4, G4 will automatically change their cell value back
to €œ0€ zero. And so on. So, regardless where you enter a €œ1€ all the other
cells will change to €œ0€ zero. Preventing a user from entering multiple €œ1€s

Thanks,
itechxxiv