Querying custom LDAP property via System.DirectoryServices in C#?

I have a custom LDAP schema installed on my OpenLDAP server which is as follows:

attributeType ( 999.0.01
    NAME 'picturePath'
    EQUALITY caseIgnoreMatch
    SUBSTR caseIgnoreSubstringsMatch
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.15{1024}
    )

objectClass ( 999.1.01
    NAME 'indieStackTeam'
            DESC 'Team definition for IndieStack'
    SUP groupOfUniqueNames
    STRUCTURAL
            MAY     ( picturePath )
    )

In my ASP.NET MVC 2 application, I'm querying for the picturePath property like so (and it is confirmed that picturePath exists in the list of keys):

this.Picture = properties["picturePath"].Value as string;

When I attempt to do this under .NET 3.5 I get the following exception:

[COMException (0x8000500c): Unknown error (0x8000500c)]   
    System.DirectoryServices.PropertyValueCollection.PopulateList() +347013
    System.DirectoryServices.PropertyValueCollection..ctor(DirectoryEntry entry, String propertyName) +49   
    System.DirectoryServices.PropertyCollection.get_Item(String propertyName) +150

However, when the same code runs under Mono (on the same server as OpenLDAP) it works perfectly fine. Clients such as LDAPAdmin can also read the picturePath property correctly.

More so, it's only when I go to read the value that it fails; I can see the property is there in the keys list, I just can't access it.

Unfortunately unknown error doesn't tell me a lot about what's going wrong, but I'm finding the .NET implementation of System.DirectoryServices is very flaky (you get the same unknown error if you connect to the LDAP server using lowercase in 'DC=').

Has anyone had this problem before and if so, how is it solved?

Two things you should check:

1) does that particular user object indeed have a value in picturePath? You might want to check for existance of the property before accessing it:

if(properties.Contains("picturePath") && properties["picturePath"].Count > 0)
{
   ....
}

2) If I remember correctly, to get access to custom attributes, you should explicitly refresh the cache for a user object before doing anything:

DirectoryEntry de = ......;  // find / assign that DirectoryEntry somehow

de.RefreshCache();  // to load all properties from the directory

or:

de.RefreshCache(new string[] { "picturePath" });  // to just load the "picturePath" attribute

Also: the classes in System.DirectoryServices are really mostly geared towards being used against Active Directory - there might be "surprises" or subtle incompatibilities when used against some other LDAP server - like OpenLDAP.