Cannot install any Custom ROMs on Xperia Ray ST18i: assert failed: getprop Status 7

When I try to install any of the roms of that page: http://get.cm/?device=urushi I always get this error: > Finding update package... Opening update package... Installing > update... assert failed: getprop("ro.product.device") == "ST18i"|| > getprop("ro.build.product") == "ST18i"|| getprop("ro.product.device") > == "ST18a"|| getprop("ro.build.product") == "ST18a"|| getprop("ro.product.device") == "urushi" || > getprop("ro.build.product") == "urushi" E:Error in > /sdcard/cm-9.1.0-urushi.zip > (Status 7) Installation aborted. This sounds to me, that the prop doesen't get the right string "ST18i" which is strange, cause that's exactly my model. Do I have to downgrade or install something else first? I also tried to install the old image Xperia Ray (ST18i)_4.0.2.A.0.42_CE.zip again, but there is just sais "installation aborted". Are there different Rescue Menues? I read, someone tried reinstalled his rescue menu with Odin. I installed my Recovery Mod with the app **x-Parts** from Google Play that app installs the CWM.