Error during creating/modifying quote using API

I am trying to create a quote using an API and then modify the quote over and over again using the same API by changing the quantities and other attributes may be. But intermittently the seeded code gives this error message and I am not able to figure out how the same piece of code works sometimes and sometimes it gives this error.

Error message in the xml returned is : 'Header Id does not exist on this record or does not match ID specified on header record.You require a valid header ID if the operation is Create'.

I wanted to figure out which piece of code and where is this error coming from to understand the exact reason behind it. To me it looks like a generic error message which could have multiple reasons.