When I try to activate my server it says [SEVERE] Exception in server tick loop java.lang.RuntimeException: Failed to check session lock, aborting

I created my server yesterday for my friends. It was very fun, and the server was running smoothly. This morning, I woke up, tried to run my server and it did not work! Heres what it said: Exception in server tick loop

java.lang.RuntimeException: Failed to check session lock, aborting
	at aho.h(SourceFile:49)
	at aho.<init>(SourceFile:35)
	at ahk.<init>(SourceFile:16)
	at ahl.a(SourceFile:78)