This is probably due to the fact that we've upgraded the Java runtime (JRE) in newer versions of SoapUI (I think it was in the 4.5 release). If you're able to connect with 4.0.1 you're probably affected by this known issue.
Later versions of the JRE has improved checking of certificates in SSL interactions. Unfortunately this causes problems for some users, likely because they have problems with their certificates or other PKI issues. Unfortunately we can't fix this without downgrading Java, which will make SoapUI less secure, but you can try running the standalone version of SoapUI with an early minor version of JRE 1.6.
Kind regards,
Manne Fagerlind, SoapUI developer
