Charter Communications Inc. filed a $150-million lawsuit Friday against Irell & Manella, accusing the prominent Los Angeles law firm of "critical errors" in completing a 1999 cable TV acquisition.

Charter's suit, filed in U.S. District Court in Santa Ana, also alleges that Irell concealed its mistakes for as many as nine months in 2002 after learning about them.

Irell has been the longtime counsel for St. Louis-based Charter and its controlling chairman, Paul G. Allen, on a variety of deals, including recent refinancings.

Charter spokeswoman Anita Lamont said Friday that the malpractice claims could not be resolved short of a lawsuit.

Irell partner David Gindler accused Allen of failing to "honor the intent" of the deal that Charter's board approved.

"If Charter suffered any loss at all, our firm was not the cause," Gindler said. "We are confident that we will prevail as the whole story emerges in court."