TO dear sir!
I'm continously getting a 'System error' message whenever I try to install some apps, such as Nokia Battery Monitor, Youtube Downloader and fMobi. This occurence only began recently after updating to Symbian Anna. I've installed many other apps and can still install other apps but I seem to have a problem with a select few. I have attempted to uninstall and reinstall the apps and also done a delete and restore after backup but still no change.
Have you tried re-installing the Anna ?
If this doesn't work, you may have to try a Soft / Hard Reset...but this will erase all data from the Phone Memory..so if you wish to do it, Back-up your data first...
P.S. Always provide your Device details..
I had this with the Belle update, imo it was caused by one or more of the apps which aren't compatable with Belle, it's possibly the same in your case where an app isn't compatable with ANNA, I'd recommend backing up your phone, reformatting it & then reinstall ANNA, then reinstall the backup apart from apps & settings; you'll have to redo all your settings from scratch & reinstall any apps from Nokia store, be aware though that depending on how old some of your apps are you may be asked to repurchase any which are older than a year or that you have downloaded more than 10 times.