Unable to find clone for op Const 16-169

[Bennie Schut]

>From time to time I receive this error:

org.apache.pig.impl.logicalLayer.FrontendException: ERROR 1002: Unable
to store alias uqusers11
        at org.apache.pig.PigServer.store(PigServer.java:536)
        at org.apache.pig.PigServer.store(PigServer.java:493)
        at
com.ebuddy.dwhmapreduce.pig.chatsessions.UniqueUsers.run(UniqueUsers.java:76)
        at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
        at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
        at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.RuntimeException: Unable to find clone for op Const
16-169( 1 )
        at
org.apache.pig.impl.logicalLayer.LogicalPlan.clone(LogicalPlan.java:139)
        at
org.apache.pig.impl.logicalLayer.LogicalPlanCloneHelper.<init>(LogicalPlanCloneHelper.java:63)
        at
org.apache.pig.impl.logicalLayer.LogicalPlanCloner.getClonedPlan(LogicalPlanCloner.java:45)
        at
org.apache.pig.impl.logicalLayer.parser.QueryParser.ForEachClause(QueryParser.java:3044)
        at
org.apache.pig.impl.logicalLayer.parser.QueryParser.BaseExpr(QueryParser.java:1328)
        at
org.apache.pig.impl.logicalLayer.parser.QueryParser.Expr(QueryParser.java:907)
        at
org.apache.pig.impl.logicalLayer.parser.QueryParser.Parse(QueryParser.java:696)
        at
org.apache.pig.impl.logicalLayer.LogicalPlanBuilder.parse(LogicalPlanBuilder.java:63)
        at org.apache.pig.PigServer$Graph.parseQuery(PigServer.java:1034)
        at org.apache.pig.PigServer$Graph.clone(PigServer.java:1077)
        at org.apache.pig.PigServer.clonePlan(PigServer.java:389)
        at org.apache.pig.PigServer.compileLp(PigServer.java:804)
        at org.apache.pig.PigServer.compileLp(PigServer.java:791)
        at org.apache.pig.PigServer.store(PigServer.java:509)
        ... 5 more

However running it a 2nd time it runs just fine. It's a little hard to
reproduce. I received this on a line like this:
uqusers11 = FOREACH uqusers10 GENERATE user_id, protocol, logincldr_id,
logintime_id;

but also sometimes on this:
uqusers6 = FOREACH uqusers5 GENERATE flatten($0), MIN(uqusers4.login) as
mindate;

so for now it mostly seems to happen on foreach statements (I'm
currently using pig trunk and hadoop 20.1)

Can anyone point me in the right direction on what to look at when
looking at errors like this.
Thanks,
Bennie.