SW error being a the part of the system state - an example to understand?
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I am trying to understand the following and deleted my previuos question as it was not proper. I would like to understand what is meant by "an error is the part of the total state of the system"? 

**Failure**: A failure is said to occur whenever the external behavior of a system does not conform to that prescribed in the system specification.  
**Error**: An error is a state of the system. In the absence of any corrective action by the system, an error state could lead to a failure which would not be attributed to any event subsequent to the error. For this reason the definition of an error is: the ***part of the total state of the system*** that may lead to its subsequent service failure.  
**Fault**: A fault is the adjudged cause of an error.

An example:
Requirement: Do not let the customer to withdraw any money if the balance is 100 or less.
The actual implementation:

    if (Balance<100)  //developer did not use =< as he should
       {
          return false;  
       }

Also it is clear that there is a **fault** as the operator < is incorrect. But what will be error (and failure)?
    
