90%(Expected) - Attended Conference.
We need to know N(Expected) to find the number.

From(1)

90%(total) > Expected. (No numbers here - Insuff)

From (2)

7 managers did not attend the conference. (Obviously this alone is not sufficient)

I am not sure here, but since (1) says, no more than 90% of all, it could be any % < 90. E IMO.

P.S: Could someone clarify if we could take it as exactly 90% of all managers for no more than 90%?

IMO:E, we are not sure on the expected managers number!

I agree with E, and would also add that even if we knew the number of expected managers, it's still possible that some unexpected managers showed up. It's pretty clear that 1 and 2 are insufficient by themselves. If you knew the total number of managers, T, then the number who came would just be T-7, from statement 2. For both statements, if you can't see it for sure, to prove insufficiency, show that at least two T values are possible with both statements true:

T=100
50 expected, 50 unexpected (satisfies statement 1)
45 expected managers attended, 5 didn't (satisfies given-90% of expected attended)
48 unexpected managers attended, 2 didn't (satisfies statement 2)
overall, 93 managers attended

T=80

40 expected, 40 unexpected (satisfies statement 1)
36 expected managers attended, 4 didn't ( satisfies given-90% of expected attended)
37 unexpected managers attended, 3 didn't (satisfies statement 2)
overall, 73 managers attended

shankar.ashwin wrote:
P.S: Could someone clarify if we could take it as exactly 90% of all managers for no more than 90%?

Yes, no more than 90 implies that the percentage is less than or equal to 90.