i disconnected battery and cant start the car

hi guys..can anyone help me?...i replaced the battery to my 535i and now i cant turn off the immobilser...the cars a g reg 535i wiv clifford alarm/immobiliser fitted (factory) i have been told theres a procedure after fitting a new battery..something about a 15 min countdown but i dont know what to do...can anyone help please?

I would leave the key in the "on" position for awhile but i am not sure how long. then try it. You could also try holding down the disable alarm button while a friend (or if you are agile enough) puts the battery cable back on. You may just want to pick up the phone and tell the local BMW dealer what is happening.