[AccessD] Digital signing

Distributing a commercial app - very occasionally the user will get a
message that the app is not digitally signed and won't open.  So there must
be some difference between those who get the message and those who don't.
 
Is there a setting to disable that message?  The app is distributed both as
a run-time and as requiring Access but I don't know if the digital signing
message is exclusive to one or the other.
 
Any help greatly appreciated.  It's suddenly become a big issue.
 
MTIA
 
Rocky Smolin
Beach Access Software
858-259-4334
www.bchacc.com <http://www.bchacc.com/> 
www.e-z-mrp.com <http://www.e-z-mrp.com/> 
Skype: rocky.smolin