This court has often noted that summary judgment should not be granted until the party opposing the motion has had an adequate opportunity for discovery. . . . The party opposing a motion for summary judgment has a right to challenge the affidavits and other factual materials submitted in support of the motion by conducting sufficient discovery so as to enable him to determine whether he can furnish opposing affidavits. . . . Generally summary judgment is inappropriate when the party opposing the motion has been unable to obtain responses to his discovery requests.