Could not log player

[lokspel]

To Reproduce
Steps to reproduce the behavior:
[11:22:53 ERROR]: [TradeSystem] Could not log player 'VortexL' with player 'Rejomy' ('Rejomy received 1x WOOD_SWORD'): [SQLITE_BUSY] The database file is locked (database is locked) [SQLite]
[11:22:53 ERROR]: [TradeSystem] Could not log player 'VortexL' with player 'Rejomy' ('Rejomy received 1x WOOD_SWORD'): [SQLITE_BUSY] The database file is locked (database is locked) [SQLite]
[11:22:53 ERROR]: [TradeSystem] Could not log player 'VortexL' with player 'Rejomy' ('VortexL received 1x DIAMOND_HELMET'): [SQLITE_BUSY] The database file is locked (database is locked) [SQLite]

Server information
This server is running PandaSpigot version git-PandaSpigot-159 (MC: 1.8.8) (Implementing API version 1.8.8-R0.1-SNAPSHOT) (Git: 03303f5)