We see it commonly with Norton products but not just their product. Quite a few Internet Security products have a component which blocks various types of processes which "they" decide are inappropriate. One of those processes may be the update application of your favorite malware removal tool.. Sometimes it's a firewall issue. Sometimes it's Parental Control.
In addition, automatic updates are only available on the "paid for" version of Malwarebytes (the "free" version must be updated manually) so I'll assume you have the paid version and if that's the case, Norton also has a "real time" spyware scanner running along with your Malwarebytes real time scanner.. That's generally not a good idea because most such programs conflict.. Most here recommend that you prevent one, or the other from running real time and use the second tool as a backup manual scanner.
It now becomes your decision on which steps to take to prevent those conflicts. Here, we use the second tool as a backup manual scanner so we can update occasionally and only when we need a "second opinion" from that scanner.
Hope this helps.
On March 29 Malwarebytes updated its software to version 1.45, after which the automatic updates stopped working. I also run Norton Internet Security (NIS) 2010 with the Parental Control add-on. I quickly discovered that both the Malwarebytes automatic and manual virus definition update functions CANNOT run if the NIS Parental Control is turned on. (An error message appears.)
I contacted Malwarebytes and was told it was an NIS problem. I contacted NIS and they could only recommend that I turn off the Parental Control function if I was going to run Malwarebytes update.(though they prefer that I remove ALL other anti-virus software when running NIS).
Any solutions? Neither software company appears to want to take any responsibility for this program conflict.