Just create the file named "DB_CONFIG" in the ".bitcoin" or "AppData/Roaming/Bitcoin" directory that contains the following:
set_lg_dir database
set_lk_max_locks 40000
The default was 10000. You can monitor the lock usage using "db_stat -e". I've tested it on an old laptop with 0.3.24 and 0.5.0. Obviously it will work with alt-coins based on the Bitcoin & BDB code. The same file should go into the respective "testnet" subdirectories.
Please don't omit the "set_lg_dir database" line. Without it you may corrupt the "_db.00?" and/or "log.*" files if you are unlucky and run the Berkeley DB utilities like "db_stat". With this line you will at worst get the error message from those utilities.
Good luck.
Edit: Oh, I forgot about the most obvious or non-obvious: restart the bitcoind/bitcoin-qt.