What does this error mean? IncorrectArgumentsError: Should not specify both keep_size and samples arguments. See the docstring of the samples argument for more details

[falk]

Yes, this seems to be a common problem (I am just now struggling with a similar issue).

Note that the intention is to remove both keywords, cf.

Value error in chains for a gaussian process

If I can add to the conversation, do not use the samples argument in v4. The plan is to remove it, see Remove `samples` and `keep_size` from posterior_predictive · Issue #5775 · pymc-devs/pymc · GitHub. If you want to generate posterior predictive samples for a subset of the posterior only, you should provide a sliced posterior to sample_posterior_predictive as shown in the api docs example (bottom of the page): pymc.sample_posterior_predictive — PyMC 4.1.2 documentation