I'm currently working with an old version of suse 11.2, but the repos for that version are not maintained anymore, so my questions is are repos of newer version compatible with older version of suse? I just added repos for version 11.4, and ran an update using zypper update, lots of stuff stopped working among the network manager, add/remove software.... are there any incompatibilities between repos and versions of Linux?

Yes, no and maybe. Some things may update from a very old version to just a plain old version.

In a real sense you aren't getting much of an improvement.
I'd think it would be best to consider a full install of the current version or at least start testing if you can run it.

I have never been a fan upgrades although you may be able to do that.

as above
yes ? , Maybe ? , no ?

BUT MOSTLY A BIG NO!!!

OpenSUSE 11.2 and 11.3 and 11.4 went End of life a bit back

11.2 - EOL - May 12th 2011
11.3 - EOL - January 20th 2012
11.4 - EOL - November 5th 2012

the repo mirrors might not be around

now the Evergreen project
https://en.opensuse.org/openSUSE:Evergreen
WAS backporting to 11.4 ( past-tents)
but Evergreen NOW is the long term support for 13.1

https://en.opensuse.org/openSUSE:Evergreen#Version_11.4



so you will need to manually edit the files in /etc/yum.repos.d


as to using 11.4 repos on 11.2

fonts from 11.4 will and some games
a few things that really never changes

but MOSTLY you will have what is called a "Frankensteined install "
a mix of two or more Operating systems
and those MOSTLY do not live long , they die a very ugly and messy DEATH

that is a symptom of a DEAD Frankenstein install


the only fix is:
reformat and REINSTALL

there is NO!!!! east way to fix it

there MIGHT be a VERY HARD way to fix ?

do you have TWO WEEKS to a MONTH !!!
a reinstall will take 30 minutes