d) I was so tired that I couldn't sleep
e) I was tired so that I couldn't sleep
Of these two examples d) is perfect and e) simply doesn't work.
d) is the correct form of e) or an alternative would be I was too tired to sleep.
One of my friends has explained this to me. Nevertheless, I couldn't get why E is incorrect.
there -- at the link-- has been written tow kinds of "so that", hasn't been written? if so, we could use them interchageably by the meaning both result and purpose.
I have underlined what I mean: