* Investors file complaint over acoustics during AGM
* Osram registration blocked, no listing in April
* Siemens applies for registration block to be lifted
* No date ever given for IPO, April was earliest possible (Adds detail on spin-off process, analyst comment)
FRANKFURT, March 15 German engineer Siemens will not be able to spin off its lighting division in April, the earliest date for the planned listing, because of legal action by a handful of investors challenging the move.
Siemens is selling off Osram as part of a restructuring which includes shedding less profitable businesses and seeking 6 billion euros ($7.8 billion) of savings.
A small group of investors is taking legal action, citing acoustic problems at the group's shareholder meeting in the Olympia Halle in Munich in January at which the spin-off and listing was approved, a Siemens spokesman said.
"Siemens considers the action to be without merit and will rigorously drive the planned spin-off and public listing of Osram Licht AG," it said on Friday.
A spokesman for the regional court in Munich confirmed a suit had been filed, but declined to give further details.
A German paper reported last month a group of nine investors planned to challenge the spin-off of Osram, whose brand is 106 years old and which has a book value of 2.3 billion euros, because of problems hearing chief financial officer Joe Kaeser at the annual general meeting (AGM).
Siemens had not given an exact date for the planned listing, but the European spring was seen as the earliest a listing could take place.
"April would have been the earliest possible date for a listing. I don't see the delay as dramatic," said Baader Bank analyst Guenther Hollfelder.
Siemens plans to keep 17 percent of the business, with the remaining 80.5 percent to be held by its shareholders. More than 98 percent of shareholders approved the plans at the AGM.
Siemens needs to spin off Osram and enter it in the commercial registers in Berlin and Munich before a public listing can go ahead. The legal action blocks this registration process, thus holding up the listing plans.
Siemens has applied to the higher regional court in Munich for the registration block to be lifted, so that it can enter it in the relevant registers.
The spokesman for Siemens said the company did not know how long it would take to have the block lifted, saying the matter was in the court's hands. No one was immediately available for comment at the Munich higher regional court.
Siemens shares were up 0.1 percent at 1140 GMT, versus a 0.1 percent decline by Germany's blue-chip DAX index.
($1 = 0.7704 euros) (additional reporting by Ludwig Burger; Editing by Jane Merriman and Mark Potter)