I have now successfully tested with open ldap for windows. Looking at the LDAP logs I think there is a bug with with WingFTP with the amount of authentications made to the LDAP server. It appears that a multiple request are sent for each session. For example if I login to the FTP that is one authentication request, if I then transfer 100 files, 100 authentication requests are made, if I then delete 50 files another 50 requests are made.
The reason I'm looking at adding resilience to LDAP is as authentication regularly fails on our server (with the correct password scripted). I now think this is due to all this LDAP chatter overloading the DC's. We have two busy WingFTP servers and the DC's are on the other side of a firewall. The way I see it, there should be one LDAP request at logon and no more.
Is this something that can be looked into? Should I raise this in the bug forum?