"I have reached the age of seventy-four while I fear upon myself the temptation of women, so how can one give a fatwa for the youth to study or work in free-mixing? Allahu Musta'aan."
Reference silsilatul huda wan noor , tape number 211.
As for Ubayd al-Jaabiree then he permits both studying and working in free-mixing, Our noble Shaykh Yahya has mentioned many times that Ubayd al-Jaabiree is not proper to give fatwa.
Ubayd's fatwa on free mixing:
http://aloloom.net/vb/showthread.php?p=32170#post32170
http://www.aloloom.net/vb/showthread.php?t=8044