Hello,
Please find further explanation of this issue below.
Hello Mt.Gox Users,
Trading was unavailable for a short period of time today. There were invalid trades taking place as well as trade orders that could not be cancelled. Therefore we had to halt the trading engine and consequently, most ask orders were cancelled.
However, we have resolved this issue and trading has now resumed. Invalid trades have been cancelled and trade orders can now be cancelled. Users who have had their ask orders cancelled are kindly requested to place their orders again.
We apologize for the inconvenience caused and we will make every effort to prevent this from happening again in the future. Thank you for your continued support to Mt.Gox.
UPDATE: After investigating, we found out that the issue is likely due to an old piece of code in the trade engine that checks for bid/ask cross (i.e. negative spread). This piece of code would check for bids and asks differences, but did not make sure that both were in the same currency.
To prevent this bug issue from recurring, we have placed some extra checks to halt trading automatically should a similar issue happen again. Thank you once again for your kind understanding in this matter.
Source:
https://support.mtgox.com/entries/21845378-resolved-outage-35046-trading-unavailableWe would like to apologize for the inconvenience caused and if your problem persists, please feel free to contact us at the Support Page.