You may as well try a hard reset per the instructions below. It costs nothing, does no harm and sometimes fixes computer related stuff.
For me, most often it is the radio that is acting up after a battery change out or something where the battery was disconnected, probably before all had gone to sleep.
Re the tranny messages, to me that is a brake light switch but since your 3 was sitting for awhile, that draws the battery down and the software gets upset, hence try the Hard Reset first. It is also a clean hands stand up kind of task.
Link re changing the brake switch:
https://www.disco3.co.uk/gallery/thumbnails.php?album=5082
Hard Reset Instructions
In brief, to start the hard-reset process, open the hood but close all doors and let your 3 go to sleep - no radio display etc and no key in the ignition. This will take a couple of minutes and do not open any doors until the reset is completed. (I find that it is often a good idea to have the driver’s door window rolled down and the key in one’s pocket whenever fooling about the vehicle.)
Also, when I play with a car battery, I remove any rings I have from my fingers, also my watch.
Have the car keys in your pocket.
Disconnect the ground battery terminal from the main starting battery.
Disconnect the positive battery terminal from the main starting battery.
The reason for this order is if a wrench or loose battery cable ends grounds to the body, no arcing or other bad things happen.
(I assume that you only have one battery in your 3. If not, disconnect the others as well and leave them disconnected until after all is done.) I have the Traxide dual battery system installed.
Connect the negative cable end to the positive cable end. (
NOT to the battery.) To do this, you will need a short length, (a foot or so), of light gauge, (14 to 18 gauge AWG, insulated stranded copper), wire to span between the battery cable ends as there is not enough slack in the positive and negative battery cables for the ends to be able to touch each other.
Hold all together for about a minute or more, (suggest at least two minutes), as you are discharging memory modules within the engine computer and elsewhere. Then it is suggested you then just let all sit disconnected for say ten minutes, (minimum five minutes), prior to commencing to put the battery cable ends back on the battery posts per the following order.
Reattach positive terminal to the main starting battery positive post.
Reattach negative terminal to the main starting battery negative post.
Start engine and hopefully none or at least fewer warning lights and the radio when turned on plays music rather than being silent.
Reset time on the radio - note that the station presets are still there as not everything is erased. Nothing much else needs resetting either.
You can also now connect up the other batteries if you have a multiple battery setup.
This is a link to a thread in disco3 re the hard reset procedure.
http://bit.ly/14WXXR1
http://www.disco3.co.uk/forum/topic19547.html
This is a link to a thread on Disco3Club re the hard reset procedure.
http://www.disco3club.co.uk/phpbb/viewtopic.php?f=67&t=3374