estat icc

[sbs]

Hello,

I am attempting to use the postestimation command "estat icc" after using xtmixed for a mixed model. However, each of my attempts ends with this error:

. estat icc
invalid subcommand icc
r(321);


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        Keywords:  r(321)
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[P]     error . . . . . . . . . . . . . . . . . . . . . . . .  Return code 321
        requested action not valid after most recent estimation command;
        This message can be produced by predict or test and indicates
        that the requested action cannot be performed.

(end of search)


I am confused by this error since I found the estat icc command in documentation specific to xtmixed postestimations published by Stata. Specifically, the documentation says:

estat icc displays the intraclass correlation for pairs of responses at
each nested level of the model. Intraclass correlations are available for
random-intercept models or for random-coefficient models conditional on
random-effects covariates being equal to zero. They are not available
for crossed-effects models or with residual error structures other than
independent structures.

Is there some reason why I would not be able to use estat icc? I am using Stata 12.

Thank you for your help.