An oft repeated mistake in NY litigation, especially in NYC litigation is that of the leave to file a late notice of claim index number trap.  Put in short, plaintiff successfully seeks leave to file a late notice of claim, and then, using the same index number, files a summons and complaint against the governmental entity. This is a mistake, and will lead to dismissal.  Unless, Wait!  CPLR 2001 may apply and allow the Court equitably to fix the problem.  So we see a similar issue in MacLeod v County of Nassau ;2010 NY Slip Op 04344 ;Decided on May 18, 2010 ;Appellate Division, Second Department .
 

"In 2007, CPLR 2001 was amended to provide a measure of judicial forgiveness for certain mistakes that a plaintiff or petitioner might make with respect to the commencement of an action or special proceeding. On this appeal, the question presented is whether the plaintiffs, who filed a summons and complaint in a personal injury action with the appropriate clerk and within the applicable limitations period, but mistakenly filed those papers under the index number assigned to a related proceeding for leave to conduct pre-action disclosure that had been previously terminated, should, pursuant to the 2007 amendment to CPLR 2001, be deemed to have commenced the personal injury action on the date of that filing, where they later paid an additional index number fee. We answer that question in the affirmative.
 

On August 14, 2007, the MacLeods, intending to commence the personal injury action against the County and certain other defendants, filed a summons and complaint with the Nassau County Clerk. However, the MacLeods did not pay the filing fee, and failed to obtain a new index number. Rather, they mistakenly filed the summons and complaint under the index number assigned to the disclosure proceeding.

On August 17, 2007, the MacLeods served the County with the summons and complaint. Approximately three weeks later, the County interposed an answer, and made certain discovery demands. In its answer, the County did not raise any affirmative defense based on the MacLeods’ mistake with respect to the commencement of a personal injury action.

Subsequently, one of the parties attempted to file a request for judicial intervention, in order to schedule a preliminary conference. At that point, it was discovered that the summons and complaint bore the index number assigned to the disclosure proceeding, which had been terminated upon the issuance of the judgment (see CPLR 5011; Towley v King Arthur Rings, 40 NY2d 129, 132). The MacLeods were then informed that the index number was "invalid" (cf. Mandel v Waltco Truck Equip. Co., 243 AD2d 542, 543).

Thus, on June 2, 2008, the MacLeods paid an additional index number filing fee, obtained a new index number, and filed a new summons and complaint under that index number. The complaint was identical to the complaint filed by the MacLeods under the index number assigned to the disclosure proceeding. "