VPN connection problem

[#1]

Suggestions welcomed....
A couple of weeks ago, a work VPN connection (Juniper Network Connect) stopped working.  In all other respects, the broadband appears to be operating, but Network Connect freezes on start up.  The VPN connection had previously been working fine for the last year and we've changed nothing around our hardware set up.
It makes no difference whether the connection is wireless or ethernet.  The VPN is connecting without issue over other ADSL internet lines.
I've talked to the Plusnet support people and they don't want to get involved in a third party software problem.  I've exhausted the work IT support issues, as we seem to have pinpointed the problem to my internet connection.  I am absolutely stuck.
Any ideas gratefully received.

[#2]

I just connected to my work VPN and it's working fine but I couldn't tell you what type it is - sorry.
The most likely thing that occurs to me is a firewall - have you changed or updated any firewall?
Do you use the PlusNet 'Surf' (or 'Safe Surf')?: https://portal.plus.net/surf/ if so, maybe try turning it off.
I experienced all sorts of connectivity issues (and a couple of problems) on my work pc recently - eventually tracked it down to the date being set wrong - i'd set it back a month by accident - might also be worth a quick check.