LDAP query problem with VB.NET

See more:

VB

active-directory

I'm running a small piece of code that populates a drop down from an LDAP query. It checks if the givenname OR the surname start with the letter that is input. e.g.

S would return sarah or smith
SM would return just smith

but not if the Job title = leaver

The code works fine, except if I want to add a not to the query

This works :-

osearcher.Filter = "(|(givenname=" & Label1.Text.ToString & "*)(sn=" & Label1.Text.ToString & "*))"

But this doesn't :-

osearcher.Filter = "(|(givenname=" & Label1.Text.ToString & "*)(sn=" & Label1.Text.ToString & "*))(!(title=leaver))"

I get a "The Directory Service is unavailable" error

Any ideas ? I'm only using the LDAP Job Title field to exclude a certain OU

What I have tried:

I cut and pasted the query into an active directory custom search and it worked fine

(e.g. the result looks like this

(|(givenName=a*)(sn=a*))(!(title=leaver))