The Inland Revenue's self assessment online website appears to have collapsed under the weight of traffic on the day before the deadline for submission of tax returns.
TaxZone readers reported that Revenue's SA Online pages could not be accessed during Sunday evening.
Most attempts made by TaxZone to access the pages during the early evening returned an error message.
A Revenue spokesman at 9 pm that he was able to access the log in pages via both the home page and the practitioner zone page.
His SA Online colleagues had informed him that there was "currently no widespead service problem" other than delays in issuing responses to returns submitted.
But TaxZone members reported various problems in response to a question posted in Any Answers early on Sunday, the day before the 31 January deadline for submission of 2004 returns.
Other readers had reported submission problems on Saturday.
Difficulties reported early on Sunday appeared to relate mostly to delays in provision of receipts.
The Revenue acknowledged at lunchtime that there were delays in sending out receipts, and there was "some slowness in the system" due to increased traffic.
But there was no general problem, a spokesman said, adding that a delay in transmission of a receipt does not alter the date of delivery of the return for the purpose of the late filing penalty.
Later comments made by TaxZone readers indicated that the Revenue's system was not accepting some returns, and several members reported that they could not access the helpline.
David Evans said: "Using Iris, the FBI system goes into a permanent loop of 'the request has been acknowledged by the Gateway' and 'polling Gateway for a response' until the system 'times out'."
Other difficulties were reported although 'Tony' had "used FBI today with absolutely no problems".
Stephen Quay said he was told by the FBI helpline: "The problem was with the computer that declines or accepts the tax returns.
"All the returns are being queued and as soon as the problem is fixed, which hopefully will be soon, they will start to be processed and the appropriate responses sent out."
Nicholas Myles complained that "all returns time out" and Graeme Morrice said no online services were available at all at 8.10 pm.