Bart,
Now you're saying that the cells must be filled left-to-right, starting with A1, and can
only be filled with "x". If that's the case, use this in the Data - Validation for cell A1:
=A1="x"
And use this in B1

1:
=AND(A1="x",B1="x")
Note that when you select B1

1, the active (white) cell of your selection must be B1. This
will allow either X or x. These will allow either x or X.
--
Earl Kiosterud
www.smokeylake.com
Note: Top-posting has been the norm here.
Some folks prefer bottom-posting.
But if you bottom-post to a reply that's
already top-posted, the thread gets messy.
When in Rome...
-----------------------------------------------------------------------
"AA Arens" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Hi earl,
>
> I am still allowed to have another cell filled, so far this cell come
> after (right of) the first cell.
> Make it possible that only one cell can be filled in from a row-array.
>
> With x I meaned only x can be filled in, no other value.
>
> Thank you for your help.
>
> Bart
>
> \
>
> Earl Kiosterud wrote:
>> AA,
>>
>> Presumably, your X is a variable -- the first cell can have any value, and a second cell
>> should be blocked. Data - Validation - Custom:
>>
>> =COUNTIF($A$1:$D$1,"*")<2
>>
>> --
>> Earl Kiosterud
>> www.smokeylake.com
>>
>> Note: Top-posting has been the norm here.
>> Some folks prefer bottom-posting.
>> But if you bottom-post to a reply that's
>> already top-posted, the thread gets messy.
>> When in Rome...
>> -----------------------------------------------------------------------
>> "AA Arens" <(E-Mail Removed)> wrote in message
>> news:(E-Mail Removed)...
>> > In a range of cells (a row), I need a data validation that block a
>> > second cell to be filled with a value. How to do that?
>> >
>> > Sample:
>> >
>> > A B C D
>> > 1 X
>> >
>> > If Cell C1 has value X, another cell cannot have a velue, unless value
>> > in C1 is deleted.
>> >
>> > Bart
>> > Excel 2003
>> >
>