Need SSL config advice for SPARQL endpoint

[cbinding]

Our server was recently configured with an SSL certificate (So now https URLs). The SPARQL endpoint continues to work for SELECT queries, but updates e.g. LOAD https://mydomain/file.rdf no longer work. I'm trying to LOAD a file which exists on the same server. A web browser can open this file directly so I know the path is correct.

The 3 errors returned are of the type:

Error: Socket error: Could not connect to "https://mydomain/file.rdf" (proxy: 0):  
in ARC2_Reader via ARC2_StoreLoadQueryHandler
missing stream in "getFormat" via ARC2_Reader via ARC2_StoreLoadQueryHandler
No loader available for "https://mydomain/file.rdf":  in ARC2_StoreLoadQueryHandler

The server SSL error log has the following 3 errors:

stream_socket_client(): SSL: Handshake timed out in /mypath/semsol/arc2/ARC2_Reader.php
stream_socket_client(): Failed to enable crypto in /mypath/semsol/arc2/ARC2_Reader.php
stream_socket_client(): unable to connect to ssl://mydomain:443 (Unknown error) in
/mypath/semsol/arc2/ARC2_Reader.php

Does anyone have any advice on how to configure this correctly? I've tried various combinations of the SSL parameters as described at the bottom of the 'HTTP Reader' wiki page, but I get the same errors each time.

EDIT: styling