Hi, I'm working on mexico pension program and at primary steps, when I want to estimate impact of program by linear regression it works but when I enter my control variables I get below results in the picture, (no observation). I read in Other topics that it can be because of string variables and omitted those but still get same error. for information I have missing data if it is a case, I read in other topic that maybe missing data can be an issue but I don't know how to resolve it. thanks.

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