st: error message in mixed models stata 9

["Herman van de Werfhorst" <H.G.vandeWerfhorst@uva.nl>]

Hello,

if I want to run a random intercept mixed model (multilevel model) with the following form, I get an error message which I don't understand: 



. xtmixed y i1 i2 g3 g4 || groupvar:
                 <istmt>:  3499  _xtm_setup() not found

where i1 and i2 are individual level variables, and g3 and g4 variables measured at the higher level in which individuals are nested (at the level of the variable groupvar). 
 
Does anyone know what   "<istmt>:  3499  _xtm_setup() not found"    means? I have updated my stata 9 very recently.


Thanks,
Herman van de Werfhorst




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