That error message is pretty common with Directory Proxy Server. Here are the reasons why:
Upon reception of a request, DPS tries to route the request to the
target data views, based on the request (base) dn. When this step fails
(misconfiguration), a "No such Object" error is returned with
additional text "The entry foo=bar is not handled by the server.
Then DPS selects the "best" directory server associated with the target
data view according to the load-balancing algorithm. If no valid
directory server is found, the error "Unable to retrieve backend SEARCH
connection" is returned.
There are 4 possible causes:
- the data source pool associated with the target data view is empty
- the data sources in that data source pool are disabled or have
search-weight/bind-weight set to 0 so they are not considered valid
servers to process search/bind operations (configuration problem)
- every data source (directory server) in that data source pool are down
- the max number of connection to every data source is reached.
If you get these errors after a brain new deployment with the OOTB dps
configuration, #1 is probably the cause: DPS default config comes with a
default data view able to handle every suffix/request. This data view
is associated with a data souce pool that is empty by default. You have
to create at least one data source object, add it to that data source
pool then set load-balancing weights.
More info are available at http://docs.sun.com/app/docs/doc/820-4809/fhktx?l=en&q=dsee&a=view