The error you're encountering is because the network loaded is a struct, not a "SeriesNetwork" or "DAGNetwork" object, which the "activations" function requires. You can read more about the function by using the following command:
doc seriesnetwork.activations
To work with this network, please refer to the documentation for the MatConvNet toolbox at https://www.mathworks.com/matlabcentral/fileexchange/47811-vlfeat-matconvnet. The functions you need are "vl_simplenn_tidy" for initializing the neural network and "vl_simplenn" for running it on an image. These functions are provided in the toolbox.
