[Mediawiki-l] Import failed: Loss of session data

[=James Birkholz=]

I'm trying to import a lot of pages (Special:Import)
but I keep getting this error:
"Import failed: Loss of session data"
Is this mediaWiki or php?
I doubt that I can modify the php settings, but if I can, what do I 
need to do (temporarily)?
If it's mW, what setting?

James