Ixia said it swung from a profit to a loss in its fourth quarter due to investment losses and other charges.

After Thursday’s market close, the Calabasas tech company reported a net loss of $18.3 million (-29 cents per share), compared with net income of $4.4 million (6 cents) a year ago. Revenue fell 12 percent to $41 million.

The company’s net loss includes an impairment charge of $15.8 million for the write down of auction rate securities. Operating expenses included $2.1 million of non-recurring charges associated with certain strategic initiatives and severance payments.

Without those charges, Ixia said it would have reported net income of $1.4 million (2 cents). As of the end of 2008 Ixia said it had cash, cash equivalents and investments of more than $206 million and no debt.

“Although our 2008 fourth quarter (was) adversely impacted by the global economic slowdown and write downs of impaired investments, we continued to generate positive cash flow from our operations,” Chief Executive Atul Bhatnagar said in a statement.

Ixia makes performance test systems and service verification platforms that enable network and telephony equipment manufacturers and other entities to test voice, video, and data services and network capability under real-world conditions.

Ixia shares were up 12 cents, or 2 percent, to $5.66 in morning trading on the Nasdaq.