Some of the used errors do not provide useful information

Description

As described in title some of the errors we use do not provide useful information. For example the ErrCouldNotMarshal just uses the store name. We should look into all the errors and refactor them, to provide some more useful information when they get thrown.

Also we could add the the type of the object in some/all? of the requests, see here for more information !332 (comment 256455). Possible solution could be to add reflect.TypeOf(var) to the errors.

• ErrCouldNotMarshal could be improved, to use more than the store name like also using an error provided by the underlying decode function