Conformability error whn using "synth" command

[César Urquizo]

Hello,

I have been trying to do a synthetic controls estimation, however I keep getting the following error message:
conformability error
r(503);

I have a balanced panel dataset with observations from 1990 to 2013 for 190 countries, with only 3 missing values in the whole dataset. This is my code:

encode countryorarea, generate(panelvar)
xtset panelvar year

**Iraq
synth gni_pc share_ag share_const share_man share_min share_others share_transp share_wholesale gcf_pbi dens_pob

I have tried removing variables, but I keep getting the same error code. I appreciate it very much if someone could help me out with this. Thank you very much in advance!

César Urquizo