it seems like you are using a version of KNIME that was (somehow) partially updated from 4.1.0 to 4.1.1. I am unsure how this can happen. Could you describe whether you are working with an update version of KNIME (4.1.0 -> 4.1.1) or with KNIME 4.1.1 freshly downloaded from www.knime.com? Which operating system (Win, Mac, …) are you on?
To make this go away you could try the following:
in KNIME go to File > Update KNIME (update all the listed extensions)
I am getting the same problem (Knime 4.1.0). A couple of days ago I noticed some Excel Writer nodes, in a couple of workflows, were marked as deprecated, so I deleted and replaced them with the latest Excel Writer. I then ran them OK and outputted & opened some Excel files. Yesterday I didn’t try these workflows, but today I ran them again and now, in both workflows, the Excel Writer node throws this error. I tried copying in an old deprecated Excel Writer into one of these workflows and that worked OK. Replacing the node with a fresh new version did not work, however.
I tend to be nervous about mass-updating my Knime (e.g. I am avoiding the Update prompts in the Welcome screen) as in the past I have clicked on these and then found that some stuff did no longer work (certain nodes got ‘left behind’ etc). Anyway, I will try updating to 4.1.1 and report back.