In a furious troubleshooting spree I found a workaround, which may not be the optimal way to do things, but it worked for me:

=SUMIFS(Intäkter!H5:H105; Intäkter!A5:A105; ">2013-09-30"; Intäkter!A5:A105; "<2013-11-01"; Intäkter!D5105; "=Översättning SVE-ENG")

I removed the "equal or greater" and "equal or less" with "greater" or "lesser", and moved the dates to the last of the previous month, and the first of the following month. And then I could add my 3rd criteria that checked the type of service and it all worked flawlessly. Such a relief In case someone has similar issues I thought I'd let the thread be and add this, instead of editing and removing the original post.

Hej LeFoah

your solution looks ok and thank you for sharing it
You can shorten it a bit using sumproduct like this for october
or replace 10 with MONTH(your_ref)

I find sumproduct more flexible than SUMIFS, but maybe it's slower

__________________
Using O365 v2503 - Did you know you can thank someone who helped you? Click on the tiny scale in the right upper hand corner of your helper's post