Unhappy [HELP] Cannot re-install system .apk, istall greyed out

so, I installed contacts+ app for android. Than I removed the original system contacts app from the device. before removing it, i did a backup with "android assistant". So today I tried to reinstall the app by putting the apk on sd card. But the install option is greyed out. Cancel option is working.

What I did:

> removed screen filter app because some reported that it worked

> put my apk into system/data/app and reboot

> selected install app from unknows sources.

> also tried these commands on adb shell


# su
# mount -o remount,rw -t yaffs2 /dev/block/mtdblock3 /system
# cat /sdcard/filename.apk > /system/app/filename.apk
# mount -o remount,ro -t yaffs2 /dev/block/mtdblock3 /system
# reboot

But none seems to have solved my problem :/ Help please

My device is rooted and its ICS. its a chienese device ( Gionee gn800 )