Research in Motion (RIM) warned yesterday it would fall short of its financial targets after taking a huge charge to write down the value of its PlayBook tablet, and the BlackBerry maker\'s shares tumbled. Aiming to drive up anemic sales of the PlayBook, RIM last month began to offer the tablet computer at sharp markdowns, forcing it to book a $360 million after-tax writedown. RIM was late to the game with its PlayBook, introducing the tablet last April, long after Apple\'s iPad had established an overwhelming dominance of the new segment. Even with the discounts, consumers have failed to warm to RIM\'s entry. RIM said it sold about 150,000 tablets in the third quarter, down from 200,000 in the second quarter. That\'s a small fraction of the 11 million iPads that Apple sold in its latest quarter. \"RIM is continuing to suffer from its Playbook endeavours,\" said CCS Insight analyst Geoff Blaber. \"It hurt RIM initially by diverting focus but muted demand is now becoming clearly visible in the financials.\" It is the latest of a series of setbacks for the company that virtually invented the smartphone category.