use "C:\Users\Desktop\301.dta", clear

. clad y1 x1 x2 x3 x4 x5 x6 x7 x8 x9 x10 x11 x12 x13 x14 x15 x16  x17 x18 x19 x20 x21 x22,ul(1.000)
[x18] not found
post:  above message corresponds to expression 19, variable x18
r(111);