Error while loading learner for inference using load_learner()

Can someone please help me with the following error?

I have trained my customized learner that learns the text given in an image and saved it using learn.export(). This creates the export.pkl successfully. However when I try to load this model for inference using the code below, I get this error-

I am not able to understand what is missing while loading the model for inference and what is the error indicating?

I have only few weeks of hands-on with fastai, so any advice would be really helpful.

Thanks in advance.