The London Stock Exchange halted trading in 243 instruments on Monday, after a server software problem affected its TradElect and Infolect platforms.\nThe problem, with the LSE\u2019s matching engine \u2013 which is the core engine that links buyer and seller trading \u2013 happened on a crucial day. The LSE was expanding its co-location services, where traders\u2019 systems are placed within metres of the exchange\u2019s datacentre in order to speed trade execution times.\nThe exchange insisted to CIO sister title Computerworld UK that this upgrade was not the cause of the problem. But it is the latest in a string of technical problems at the exchange that has frustrated traders.\nMonday\u2019s problem began at 3.12pm, and trading in one in 12 instruments was halted for the rest of the day. Instruments affected included commodity trades such as heating oil, wheat, sugar, gold and platinum, as well as company shares including BP and Severn Trent. All are said to be trading normally now.\nAccenture, the outgoing services provider to the LSE that also fixed the problem, declined to comment on the technology affected. The company created and runs the soon-to-be-scrapped TradElect platform, based on Microsoft .Net architecture.\nThe LSE also runs Microsoft Windows Server 2003 software on its servers, but it is unknown if that software or Microsoft .Net architecture was at fault. Microsoft had not provided comment at the time of writing.\nHP, whose ProLiant servers are the back office hardware for trading at the LSE, said its servers were not at fault.\nEurope\u2019s oldest independent bourse declined to comment. In a notice to traders, the LSE said yesterday that it was working \u201ctowards a full resolution\u201d of the issues.\nIt is the latest in a string of technical problems at the LSE. Five weeks ago, a data glitch led to the LSE having to temporarily suspend trading in some FTSE 100 stocks, after invalid data was found in the Exchange\u2019s core TradElelect and Infolect systems. The exchange said at the time that its technology was not at fault.\n\n\n\n\n\n\n\nA year ago, it experienced serious problems with electronic trading, when network software problems took TradElect offline for a potentially devastating seven hours.\nThe exchange is moving away from its Microsoft .Net architecture to a Linux-based setup, following its \u00a318 million acquisition of Sri Lankan technology supplier Millennium IT in September. It is currently bringing IT in-house and away from existing suppliers.\nAt the time, Microsoft said it "continues to support some of the most demanding, mission-critical environments in the world and is constantly raising the performance bar with new solutions".\nIt said it had completed three different proof-of-concept projects "for a major international stock exchange", using Windows Server 2008 and Microsoft .NET.