everyone! 
So, I've been trying to fit a LMER for my data, which I fully described [in this post][1] .
This post, therefore, is a follow-up from the previous one. There's something intriguing me, I don't get any errors when I run this ANOVA:

```
aov(SCORE ~ LANGUAGE * YEAR + Error(SUBJECT/LANGUAGE * YEAR), data = data)
```

but I'm getting the boundary error (specifically for the language variable) in this model: 

```
lmer(SCORE ~ (YEAR * LANGUAGE | SUBJECT), data = data
boundary (singular) fit: see help('isSingular')
or
lmer(SCORE ~ LANGUAGE * YEAR + (YEAR | SUBJECT) + (LANGUAGE|SUBJECT), data = data
boundary (singular) fit: see help('isSingular')
``` 

As far as I'm concerned, this lmer should resseamble the repeated measures ANOVA I've ran before, so why do I get an error for the model, but not for the Anova? 

Any thoughts on it would be much appreciated. Thanks in advance!

  [1]: https://stats.stackexchange.com/questions/586633/fitting-a-lmer-with-longitudinal-data-for-2-categorical-predictors