I am using this plugin in combination with worldguard region effects and it just doesnt work

then you are doing it wrong, it works well.

I meant 1.7 builds of worldguard then, it worked one day, I updated worldguard for 1.7, and it stopped working

until now there isnt even any official wg version for 1.7, see here: http://dev.bukkit.org/bukkit-plugins/worldguard/ (correct me if im wrong)
i am running wg 5.8 with wg custom flags and some flag-plugins on my 1.7 server, too. it's running properly.

does the version info contains "with custom flags plugin", when you type "/wg version" ?

I am using 1262 from here http://builds.enginehub.org/job/worldguard/

yes it does say worldguard with custom flags

this is the region: http://gyazo.com/0c6c99a5ee86d390a61a0fe3630ba92f

however I do not get the appropriate potion effect

I figured out the problem, thanks though

just tested it with the same value... damage_resistance 100
works wonderful for me.

wg custom flags: version 1.6
wg region effects: version 1.4

maybe you just need an update of these?