WARNING Timer FORAGING raised exception

Is it normal to keep getting these warnings every few seconds from NIS:

2015-04-08 02:28:28.319 WARNING Timer FORAGING raised exception: java.lang.IllegalArgumentException: importance not set at wanted height
java.util.concurrent.CompletionException: java.lang.IllegalArgumentException: importance not set at wanted height
        at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:273)
        at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:280)
        at java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1621)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.IllegalArgumentException: importance not set at wanted height
        at org.nem.nis.state.AccountImportance.o(AccountImportance.java:128)
        at org.nem.nis.kx.k(BlockScorer.java:94)
        at org.nem.nis.kx.b(BlockScorer.java:73)
        at org.nem.nis.p.vx.a(BlockGenerator.java:66)
        at org.nem.nis.p.cq.gH(Harvester.java:54)
        at org.nem.nis.p.ko.a(HarvestingTask.java:41)
        at org.nem.nis.boot.PeerNetworkScheduler.c(PeerNetworkScheduler.java:99)
        at org.nem.nis.boot.PeerNetworkScheduler$$Lambda$227/840805047.run(Unknown Source)
        at java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1618)
        … 3 more
(org.nem.core.async.NemAsyncTimerVisitor b)


What is this warning and how to fix it?

No it is not normal to get those warning. You probably need to restart NIS.
With what account are you harvesting?

Windows 10 I am getting the same symptom.

After opening the firewall port 7890, it appears the message went away.

Or it went away for another reason. Delegated harvesting takes 360 blocks to be active.