Trying to connect to a Citrix XenApp/XenDesktop farm via Citrix NetScaler Gateway from an iOS device might lead to recurring authentication (in my case twice) and after trying to start an app the Receiver will soon present the message „error could not connect to server“.
If you are sure that your installation worked fine just some time agoe it is most likely that a bug in the current (6.1) Citrix Receiver causes this issue. I found several discussions about this and the only solution so far seems to be to use the Citrix R1. Initially I believe the R1 was build for testing new releases but it seems that at least for now it still is an older version (6.0.1).
You can download the Citrix R1 here, which solved at least my issue with „error could not connect to server“ on my iOS 9.0.2 device.
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