These can be tough to solve. Did you open the laccdb file you speak of to see how may entries are in it? IIRC, all of these operations require Access to close the db, perform the operation and then re-open the db. If the lock file has 2 entries in it, one of them is a left over if no one is actually in it. I haven't seen this happen when the db is in a local directory but I have seen issues with the lock file when the db is in a network directory, even when not split.
I'm assuming there are no folder permissions issues for you (you need the whole 9 yards - create/read/write/modify/delete) and that it's not about Trusted Locations either.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.