Difference between these two terms.

Outside of a slight emphasis on the negative when you use "not," there is no difference in this example between the two usages.

There is no difference between them.

"Please look into this matter" sounds better.

Thanks Jgweed for replying. Just one last question, is the use of gerund "being" is needed before the word able? If no, then why not? Sometimes it comes, sometimes not. Can you tell me something about it so that I could figure out where to use "being" before the word "able" and where not to?

Thanks and regards

Again, it is the verb time you are concerned with.

I have been able . . .

I have not been able. . .

I am not able
I regret not being able.

I was absent
I wish I had been present

Not being over six feet tall, I'm no good at basketball.

Are these examples any help?

Thanks that helped Any more replies are still welcomed, though