I want to store a structure in the tag field of a treenode.

I create the structure, assign values to variables in the structure and then assign the structure to the node. This all works great untill I want to change a value within the structure by access the node.

I get the error "Expression is a value and cannot be a target of an assignment" when I try the code below

CType(nde.Tag, SG_DATA).AllowableID = row.AllowableSpeciesID

and if I try the following ...
sgData = CType(nde.Tag, SG_DATA)
sgData.AllowableID = row.AllowableSpeciesID

At runtime the value of the AllowableSpeciesID is changed in structure object sgData but not in the node tag object. It seems as if I cannot get a reference to the stored object.

Is there something I am missing?

Any suggestions....