RIM (RIMM) expects earnings in the fourth quarter to be at the low end of its earlier target of 83 cents to 91 cents a share. An interesting data point to consider in light of the company’s claim that it had “record levels” of net subscriber additions during the month of December and predicts subscriber additions for the quarter ending Feb. 28 to be more than 20 percent higher than previously estimated.

“RIM achieved a very strong start to the holiday buying season and the momentum carried on stronger than expected during the past seven weeks despite a seasonally slower time frame and the challenging economic environment,” co-CEO Jim Balsillie said in a statement. “We are pleased with our leadership and momentum in the market after shipping our 50 millionth BlackBerry smartphone in January and introducing a range of new products that are achieving exceptional early results and helping attract record levels of new customers to the BlackBerry platform.”

Unfortunately for RIM, those “exceptional early results” and “record levels of new customers” don’t appear to be enough to ease investor concerns that its profits are waning. Shares in the company slid more than 17 percent in early trading today.

A likely explanation. There’s little doubt the botched debut of the new Blackberry Storm undermined RIM’s performance this quarter. But perhaps there’s something more at work here as well–like the quality of RIM’s handsets themselves. “We think an additional factor is a poor reception to the much-anticipated Storm and Bold,” analysts at Deutsche Bank wrote in a client note. “We think the Storm has numerous flaws and the functionality of both devices is largely unchanged from previous devices.”