Weird exception for high connection pool size

[anidotnet]

I was deploying a simple restful web service in Openshift. When I set below settings for db I am getting an error mentioned below:

Settings: { "address" : "mysql.async",
"connection" : "MySQL",
"host" : "127.13.0.2",
"port" : 3306,
"maxPoolSize" : 300,
"username" : "root",
"password" : "*******",
"database" : "blog"
}

Error: [vert.x-eventloop-thread-3] 2014-04-11T00:57:57.922-04:00 WARNING [io.netty.channel.DefaultChannelPipeline] An exception was thrown by a user handler's exceptionCaught() method while handling the following exception:
io.netty.handler.codec.DecoderException: java.lang.NoClassDefFoundError: com/github/mauricio/async/db/util/ByteBufferUtils$
at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:259)
at io.netty.handler.codec.ByteToMessageDecoder.channelInactive(ByteToMessageDecoder.java:192)
at io.netty.channel.DefaultChannelHandlerContext.invokeChannelInactive(DefaultChannelHandlerContext.java:240)
at io.netty.channel.DefaultChannelHandlerContext.fireChannelInactive(DefaultChannelHandlerContext.java:226)
at io.netty.channel.DefaultChannelPipeline.fireChannelInactive(DefaultChannelPipeline.java:767)
at io.netty.channel.AbstractChannel$AbstractUnsafe$5.run(AbstractChannel.java:567)
at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:354)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:353)
at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:101)
at java.lang.Thread.run(Thread.java:744)
Caused by: java.lang.NoClassDefFoundError: com/github/mauricio/async/db/util/ByteBufferUtils$
at com.github.mauricio.async.db.mysql.codec.MySQLFrameDecoder.decode(MySQLFrameDecoder.scala:63)
at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:228)
... 9 more

But when the maxPoolSize = 10, it is working fine, no such exception. Moreover, for my local Windows MySQL installation I am not seeing such things for high connection pool size. What is the reason for this?

[Narigo]

Sorry for the late reply, @anidotnet - I believe this has something to do with OpenShift, but I don't know much about it.

Does the exception occur on deployment or while sending more than X commands to the server?
Maybe OpenShift disallows too many connections?

[anidotnet]

Thanks for the reply. This error occurred during the deployment time. But still I am not sure why a NoClassDefFoundError.