I have a strange error with "sdmxuse" command. I used the same code a week ago with no issues. Now I cannot use the OECD API..

Code:
 
sdmxuse datastructure OECD, clear dataset(KEI)
Now I see error, "sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderE xception: unable to find valid certification path to requested target"

I am trying to find the reasons, but I keep getting Java questions and answer..
Does anyone know why I am getting the error?