Error message in lme4::glmer: “ 'what' must be a character string or a function”

Question

I am running a multi-level model. I use the following commands with validatedRS6 as the outcome, random as the predictor and clustno a

Answer 1

(expanded from comment).

Congratulations, you found a bug in lme4! This is fixed now:

https://github.com/lme4/lme4/commit/9c12f002821f9567d5454e2ce3b78076dabffb54

It is caused by having a variable called new in the global environment (deep in the guts of the code, lme4 uses do.call(new,...) and finds your variable new rather than the built-in function new).

You can install a patched version from Github using devtools::install_github() (but you'll need compilation tools etc.). Alternately, there is a very simple workaround -- just call your variable anything other than new (you can't just copy it, i.e. new2 <- new -- you also have to make sure the old version is removed (rm("new"))).