http://kb2.adobe.com/cps/930/cpsid_93026.html resolved the problem for me
Known issues for version 10.1.2
For a list of current issues, see http://kb2.adobe.com/cps/877/cpsid_87775.html.
• 2951429: Ink Manager color swatches are broken, display in RGB, most spots missing.
• Printing workarounds for the issues below appear at http://kb2.adobe.com/cps/928/cpsid_92870.html:
• The printing preference to print on both sides of the paper is on by default.
• Reader crashes when trying to print when Protected Mode is on.
• Acrobat X Professional crashes on close | Preflight panel access: See http://kb2.adobe.com/cps/928/cpsid_92893.html
• PDFs in a browser appear as a grey box and don’t display when sent via HTTPS/SSL: For a hot fix and workaround, go here: http://kb2.adobe.com/cps/930/cpsid_93026.html.
• Some plugins that rely on HFTs may cause a hang or crash. For example, the LeanGreen plugin does not work. Acrobat 10.1.2 crashes when closing Acrobat after accessing Preflight panel.
Thanks, I'll give this a try, although if it works, how do I deploy it to 20,000+ public end users of whose workstations I have no control over? Whilst Adobe have indicated the fix will be available in the next quarterly comfort, it is cold comfort for me as our clients move in droves back to paper lodgements. It's putting huge pressures on our internal processing teams and costing our organisation big time.
Hopefully 10.1.3 does not contain any significant bugs.
I think I solved the problem for my website my turning off gzip compression for pdf files in my htaccess file
SetEnvIfNoCase Request_URI \.pdf$ no-gzip dont-var
Hope that helps someone!