TS 4.0 charts stopped updating: why?

[Simon Campbell <s.campbell@xxxxxxxxxxx>]

For seemingly no reason (my datafeed reception was just fine, & quotes
continued to come into my Signal box as evidenced by it's LCD display)
....my charts as well as the server clock just stopped updating.  I had to
shut down TS and start it up again to get it back to normal (I have have a
gap in my charts).

This had happened a few times over the last week or so.  

Any explanations?  What can I do to prevent it happening again?

Rgds
Simon.