Dear Statalist,

I have a question about the error message in the title. It's really mysterious to me...

I'm trying to run a regression in which all independent variables are fully interacted with race. So, I tried the following:

Code:
reg empl x_wht x_blk x_hsp (i.cty i.yr)#i.rac, vce(boot)
And I've got the error message. What I don't understand is that the following worked!

Code:
reg empl x_wht x_blk x_ors i.cty#i.rac i.yr#i.rac, vce(boot)
Could anyone tell me the reason? I'll really appreciate.