Replace the battery and remember which button does what:chair:Well it works with some keys not with others. All keys I have for it can start the car and open every other door but the drivers door (I think one pair still can). The FOB's battery died so I never bothered with it (also the paint that says lock/unlock is gone and I can't tell difference). It worked last week fine.
On my 99 same generation as yours I found the following.
If the keys are not the OEM keys with the black plastic tops, they are likely recut keys. Since a lot of locksmiths don't carry Subaru blanks they'll use a Toyota blank which will work in the ignition no problem but can be finicky in the door locks. I had this problem and had the locksmith check it out, 2 out of 3 times the lock wouldn't open but occassionally it did. Found the same thing that the key appears to go in deeper in the door locks than the igniton. I also found if I kept the door locks lubed it worked more often, just don't use WD40 it'll freeze. 99% of the time I used the remote.
And if someone says they didn't get a remote when they bought their car, get one off ebay that will work with your year, it's that simple.