xtgee repeated time values within panel in corr(AR1) and corr(unstr) but not in corr(ind) and corr(exc)

[krudy]

I am trying to run a xtgee model, and have made sure to have unique panel (Employee-Year).

However, when I specific corr to be AR1 or unstr, it gives the error msg "repeated time values within panel"
xtgee y x1 x2 x3 Experience Year, family(gaus) link(iden) i(FirmID) corr(AR1) t(Experience)
xtgee y x1 x2 x3 Experience Year, family(gaus) link(iden) i(FirmID) corr(unstr) t(Experience)

But, if I specify corr to be ind or exc, I do not receive any error msg.
xtgee y x1 x2 x3 Experience Year, family(gaus) link(iden) i(FirmID) corr(ind) t(Experience)
xtgee y x1 x2 x3 Experience Year, family(gaus) link(iden) i(FirmID) corr(exc) t(Experience)

Any idea why? Many thanks in advance.

[Jorge Eduardo Perez Perez]

Are you completely sure you don't have repeated time values within panel? Try isid employee year and see if it returns an error message.
Can you replicate this with a Stata dataset or can you upload a sample of your data?

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