MongoDb Java driver - MongoException$Network: Read operation to server localhost:27017 failed

We started getting the below error intermittently during the last week. So far we could not trace this problem to anything in particular. The query in question is an aggregation to a collection which has around 400k objects. We have the same application running for different clients and it started happening to clients which have passed that 400k mark. I ran the query directly and it took about 1.5 seconds. The same exact exception took place when we were iterating over the results of another aggregation:

DBCursor cursor = db.cMD.find([colaborador: [$in: listP], data: data], [colab: 1, _id: 0])
def listW = []
while (cursor.hasNext()) //Exception happened here
{ def resultMap = cursor.next().toMap() listW.add(resultMap.colab) }

2015-05-20 14:03:43,511 [quartzScheduler_Worker-6] ERROR listeners.ExceptionPrinterJobListener - Exception occurred in job: Grails Job
org.quartz.JobExecutionException: com.mongodb.MongoException$Network: Read operation to server localhost:27017 failed on database application1 [See nested exception: com.mongodb.MongoException$Network: Read operation to server localhost:27017 failed on database application1]
at grails.plugins.quartz.GrailsJobFactory$GrailsJob.execute(GrailsJobFactory.java:111)
at grails.plugins.quartz.QuartzDisplayJob.execute(QuartzDisplayJob.groovy:27)
at org.quartz.core.JobRunShell.run(JobRunShell.java:202)
at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:573)
Caused by: com.mongodb.MongoException$Network: Read operation to server localhost:27017 failed on database application1
at com.mongodb.DBTCPConnector.innerCall(DBTCPConnector.java:300)
at com.mongodb.DBTCPConnector.call(DBTCPConnector.java:271)
at com.mongodb.DBCollectionImpl.find(DBCollectionImpl.java:84)
at com.mongodb.DB.command(DB.java:317)
at com.mongodb.DB.command(DB.java:296)
at com.mongodb.DBCollectionImpl.aggregate(DBCollectionImpl.java:99)
at com.mongodb.DBCollection.aggregate(DBCollection.java:1571)
at com.gmongo.internal.Patcher._invoke(Patcher.groovy:49)
at com.gmongo.internal.Patcher$__patchInternal_closure1.doCall(Patcher.groovy:38)
at 
OUR APPLICATION CODE
at GrailsMelodyGrailsPlugin$_closure4_closure16_closure17.doCall(GrailsMelodyGrailsPlugin.groovy:184)
at 
OUR APPLICATION CODE
at grails.plugins.quartz.GrailsJobFactory$GrailsJob.execute(GrailsJobFactory.java:102)
... 3 more
Caused by: java.net.SocketTimeoutException: Read timed out
at java.net.SocketInputStream.read(SocketInputStream.java:152)
at java.net.SocketInputStream.read(SocketInputStream.java:122)
at java.io.BufferedInputStream.fill(BufferedInputStream.java:235)
at java.io.BufferedInputStream.read1(BufferedInputStream.java:275)
at java.io.BufferedInputStream.read(BufferedInputStream.java:334)
at org.bson.io.Bits.readFully(Bits.java:48)
at org.bson.io.Bits.readFully(Bits.java:35)
at org.bson.io.Bits.readFully(Bits.java:30)
at com.mongodb.Response.<init>(Response.java:42)
at com.mongodb.DBPort$1.execute(DBPort.java:141)
at com.mongodb.DBPort$1.execute(DBPort.java:135)
at com.mongodb.DBPort.doOperation(DBPort.java:164)
at com.mongodb.DBPort.call(DBPort.java:135)
at com.mongodb.DBTCPConnector.innerCall(DBTCPConnector.java:292)
... 16 more

Any ideas?