Upgrading Citrix NetScaler 10.5 to 11–SharePoint Websites might fail to load

During the last weeks I was facing a really strange problem. After upgrading a NetScaler from Version 10.5 to 11 one specific SharePoint Website was not accessible any longer. Either it looked like this – so it was not completely loaded:

(As you can see the browser showed “ERR_CONNECTION_ABORTED”.)

Sometimes it even directly stopped when “Is loaded” was shown.

Interestingly other websites – opened through the same NetScaler – worked without any problems. Furthermore there were no specific Actions / Policy bound to the Virtual Server – it was just a load balancer.

We tested different things and even debugged our Backend-Systems. Unfortunately we didn’t find any problems. Luckily one day I discussed the problem with a Citrix SE. He told me that he was facing the same problem when the NetScaler Insight Center (and so AppFlow) was used to monitor a Virtual Server. I checked the Insight Center and guess what – the Insight was enabled for the Website which failed to load after the NetScaler Upgrade.

So i disabled the monitoring – upgraded the NetScaler – checked the website – Problem fixed
I still don’t get why AppFlow prevents loading a load balanced WebSite – but if you have problems like that just try to disable AppFlow.