Cache Translation Object: Non-consistent locale value! Plugin collision?

here is the new error message: `Cache Translation Object debug info
—– start here —–
Enabled: 1
Type: file
Object cached: bool(false)
Current locale: string(5) “en_US”
Admin Warning: Cache Translation Object: Non-consistent locale value (previous: en_US, now: )! Plugin collision?`

as to other language related plugins, I use http://wordpress.org/extend/plugins/qtranslate/ and this theme: http://themehybrid.com/themes/skeleton

seems to work. now mroe errors and I see this:

Caching Active (5878 bytes cached)

anything else I can check to see if it really improves anything? the site I am testing it on is: http://www.quilombobrasil.com