PHP: Setting a different lead owner

Hi guys,

I  use PHP to login into MsCRM and add leads. This all works and the leads are logged successfully into MsCRM.

I use my own account for logging the leads, but I have some issues while setting another lead owner not myself on them. The interesting thing is that I can set a different lead owner using some users but I can't using others. I checked the user properties and attributes and I just can't find why I can set certain users to lead owner but have problems with the rest.

Can you please clarify for me, what I should check for to solve this issue ?

 Thank you,

Mircea.