Hi All,

I often find solutions on this site to my excel woes but I've come across a problem that is probably a simple fix but my google-foo has let me down and not found an answer for so I thought I would sign up and turn to you lovely folks.

I'm using the re-purposed custom data validation formula (stolen from elsewhere on the interwebs) below to allow only specific characters in a text cell which is working great:

=IF(ISERROR(SUMPRODUCT(SEARCH(MID(AW2,ROW(INDIRECT("1:"&LEN(AW2))),1),"0123456789 -/\()abcdefghijklmnopqrstuvwxyz"))),FALSE,TRUE)
However I now need to allow apostrophes in this cell as well but simply adding ' to the list of characters does not work and I've tried escaping it by adding /' or '' or "'" none of which seem to be doing the job.

Can someone slap me up side the head and point out my obvious mistake?