ColdFusion Error: Session.SessionID Not Defined?

you have session management turned on in your cfapplication tag?

If you're using application.cfc (instead of .cfm)  are you doing this command in onApplicationStart or onApplicationEnd  or onSessionEnd ?   Session variables are not available directly in these functions

Yes I have session management turned on.

I'm using application.cfc. I'm not calling session.sessionid in this file at all. It does get called outside of this file though.

is there something in your code that clears session variables

do you have clear the session structure (perhaps for logout?)

I would start by placing a test at the start of onRequestStart to see if the session.sessionID is defined there (before the bulk of your code is executed)

What version of Coldfusion are you using?   I think session.sessionID started with MX ?

Yes, when the login times out, it calls a function that clears the session variables, but then it redirects them (cflocation) back to the login page. This would be another request, correct? So a new sessionid would be defined?

I'm using CF 8.

By the way, I can't reproduce this error, several users are getting this error though.

I have never felt comfortable clearing all session variables because some are used by the system and we can't predict when they are re-created or used.

Coldfusion places cookies to maintain the session, they don't use the session variables directly for session management, they are more like an FYI for us developers.   I am referring to CFID, CFTOKEN and sessionID.    I suspect if you were to kill the cookies, the session may be recreated, but I can't say that clearing out the session variables only would cause them to be recreated (because the cookies still exist).

I have always just cleared the variables that I use.   To make this easier, I add a structure within session to manage this...   session.login.userID  and then just delete the login structure and leave the rest of the session alone..

I can't really recode the whole app to use a different session variable structure. This app is HUGE.

I could just do away with the StructClear(Session) statement but I don't want any old session data hanging around if the user logs out.

Any other suggestions?

That looks good. Should I also include urltoken since that's another built-in variable?

sure, makes sense...

And if there are any that you are maintaining that you don't want to lose, perhaps the session start date/time or something..