Adding node error

I have 2 different corpora in my Local Corpus, and about 90 sessions described in total.
I just added a new session, but now I can neither add a ‘content’ node or a ‘project’ node to this new session, their icons are grayed.
I tried draging a ‘project’ from the Favourites to my session but I got this message ‘The maximum nodes of this type have already been added’.
How many nodes (of which types) are allowed in Arbil ? Why this limitation ? I tried to create a new corpus, it is the same.
Thanks for helping

Hi,

An IMDI Session can have only one Project node and one Content node. If you want to add one of these from favourites, delete the existing node from the target Session first (you can do so by right clicking the node in the tree and selecting ‘Delete’).

These limitations come from the IMDI schema. More information can be found at http://www.mpi.nl/IMDI/
If using another metadata format is an option for you, you might consider using CMDI and define your own metadata structure. More information about that can be found at http://clarin.eu/content/component-metadata

Hope that answers your question!
Best,
Twan