Research in Motion today reported its internal probe of stock option grants is taking longer than expected, in part, because it has found a quarter of a million new documents to examine.

In a letter to the Ontario Securities Commission, RIM said it is reviewing 650,000 electronic documents — up from an earlier estimate of 400,000.

RIM launched a voluntary internal probe of its stock option grants in September. At that time, it said earnings would have to be restated going back to 1997 by a total of US$25 million to US$45 million.

It later warned that the restatements will be higher than that, but it couldn’t say how much higher.

The OSC has given RIM until March 5 to make all of its required financial filings. In the meantime, a cease trade order will continue to apply to the company’s insiders. But the stock can continue to trade on the TSX and the Nasdaq.

RIM said it expects to meet this Thursday’s deadline for filing its preliminary third-quarter financial report.

The OSC and the U.S. Securities and Exchange Commission are also looking into the RIM stock option files.

Shares of RIM rose $2.17 to close at $157.17 on the TSX.