Conversation so far:
Did U and  Don't Don by Super Junior have success?
Super Junior's U exceeded 400,000 downloads within five hours of release. Don't Don became the second best-selling record of 2007.
DidSuper Junior go on any tours during 2006–2007 with U and  Don't Don?
Are there any other interesting aspects about this Super Junior article besides that U exceeded 400,000 downloads within five hours of release and ultimately surpassed 1.7 million downloads, crashing the server?
In late 2006, Kyuhyun, Ryeowook, and Yesung formed the subgroup Super Junior-K.R.Y., Super Junior's first sub-unit.
Was subgroup Super Junior-K.R.Y., Super Junior's first sub-unit also successful?
Super Junior-K.R.Y. performed their first single The One I Love, theme song to the Korean television drama Hyena, on the KBS music program Music Bank on November 5, 2006.
How many copies or downloads were sold of U by Super Junior?
Super Junior's U ultimately surpassed 1.7 million downloads, crashing the server
Did the Super Junior-K.R.Y., Super Junior's first sub-unit release any other hits or albums?
Super Junior released their first single Rokuko on February 23, 2007, and made a debut performance on Popular Songs two days later.
What happened with Super Junior after the release of U, in 2007?
Super Junior's Don't Don was not released until September 20, 2007.
Why was Super Junior's second official album released on this date, did it get delayed?
Super Junior's second official album was intended for a late 2006 release, but due to several accidental setbacks, Don't Don was not released until September 20, 2007.

Question: What accidental setbacks happen at the time?
Self-contained rewrite: What accidental setbacks happened at the time to Super Junior delaying the release of Don't Don to September 20, 2007?