Writing ArcObjects code and using an Access personal geodatabase will result sooner or later in an error along the lines of “Cannot aquire a schema lock because of an existing lock.” Spending hours going through code, making sure objects are disposed of and that all connections closed often makes very little difference. It becomes apparent some of the problems lie deeper than customised code when the same errors occur when using ArcMap or ArcCatalog without any modifications.
I have been using Unlocker, a freeware program, to solve these issues when developing with ArcObjects (or just using ArcMap..). Once installed a simple right click on an ldb or mdb file can remove any file locks, and your code is free to run again. It works with any Windows file or folder so is a useful program to have around even without geodatabases.
More reviews and an alternative download site can be found here.