The company confirmed a BBC report on Thursday that a worker reported a "rough ride" on the line outside the station on the evening before the 10 May crash.
But it described as "speculative" the suggestion that its staff wrongly instructed maintenance workers to inspect the line towards London, when the problem had been detected on the line from London.
BBC transport correspondent Simon Montague reported that an off-duty rail worker travelling home from London contacted Railtrack signal control at King's Cross.
Railtrack staff passed the report to its maintenance contractor Jarvis in York. But Jarvis says tape recordings show that its staff were told to inspect the up line, towards London.
No fault was found.
On Thursday, Railtrack said in a statement: "The investigation is looking at the communication process that took place between all the rail industry staff involved.
"Currently, the tapes of the conversations are with the police as part of their investigation and it would be inappropriate to comment while they continue their inquiries."
Loose nuts
The police and crash investigators are examining the communications between the two companies.
They want to know whether the loose nuts which caused the crash might have been found, if the correct, down line from London had been checked.
Railtrack says it cannot confirm the instructions given to Jarvis but the maintenance company says it was not told to inspect the down line.
The company has withdrawn an earlier assurance that Jarvis did inspect both lines.
Bob Crow, the general secretary of the RMT union, said: "This is systematic of the chaos of maintenance on the railways created by the fragmentation of the rail network.
"You have contractors using sub contractors, sub contractors using agencies, agencies using casual staff and they are all in it for money, not safety."
Faulty points
Seven people died and dozens were injured when the King's Cross to King's Lynn passenger service came off the tracks as it passed over the main faulty points.
Last week, Transport Secretary Alistair Darling condemned track around the station as "appalling" following the publication of a damning new report into the accident.
The second interim study into the disaster concluded up to 20% of nuts on nearby sets of points were not fully tightened at the time.
Bereaved families have repeatedly called for a full public inquiry into the crash.
Louise Christian, the solicitor acting for some of the families said relatives had contacted her about the latest revelations and were "absolutely appalled".
"No-one has admitted liability for this crash and while Railtrack and Jarvis are playing this blame game it is the victims who are suffering.
"It underlines the need for a public inquiry because this process isn't open or transparent."
~RS~a~RS~International~RS~q~RS~~RS~z~RS~41~RS~)