how do you know if a ies light is up to a 90 degree angle? yes i get that error message i use the sample ies files form this site and they work fine. but i have my own hundreds of ies i like to use. but that error message keeps popin up about the angle

You know that the angle isn't supported if you get that error message... that simple

Glare already worked out some IES improvements that also raise the supported types:
viewtopic.php?f=7&t=11577

Perhaps the best workflow, would be to use a ies program load the ies and save it again, some of these editors save only in 90º, so you have all your ies working.