This post talks about ORA - 01436 : Connect by Loop in User Data and how it happens. It basically discusses about three points:

1) What does the error code mean?

2) How to simulate this error?

3) How to debug when this error code is encountered?

It is available here.

http://thinktibits.blogspot.com/2008/07/so-what-is-problem-i-got-error-ora.html

TO_YMINTERVAL explained with examples:

http://thinktibits.blogspot.com/2008/06/toyminterval-date-manipulation.html