How to cope with nested random variables

[fulviomissoni]

Hello,

I've data with two nested grouping variables and one fixed effect. In particular, I'm interested in error committed by each subjects (first random effect) as distance varying (fixed effect).

Each subject is tested five times with twelve different stimulus (second random effect, nested in subject).

My model is as follows:
model <- lme4(err ~ distance + (distance|stim:subj))

I would to obtain a simple plot with a single line for each subject taking in account random effects so:
preds <- estimate_relation(model, include_random = TRUE)

But, I get an error:
Messaggio di avvertimento:
include_random was set to TRUE, but not all random effects were found in data. Setting include_random = FALSE now.

How can I cope with that situation?

Thank you