#N/A errors are caused both at the backend (e.
g.
spaces in entries of the index column) and at the Frontend (e.
g.
misspelled text entered in lookup_value).
Here you will see how to enter the different types of data in lookup_value argument so you don't receive an unwanted error by such cause again...
How to enter Dates in lookup_value First, you must enter a date in the referenced cell in the correct order.
For example: A2 with 01/31/2009 is a date while 31/01/2009 not.
Second, enter dates in the correct format, for example: A2 with 02SEP09 is not a date.
Convert this string into a serial number date by using functions: MID, LEFT, RIGHT.
Finally, if you hard code the date, do it properly, do it this way:

• =VLOOKUP(40091,...
  ) You can enter a number that represents a date serial number
• =VLOOKUP(DATEVALUE(""10/5/2009""),...
  )
• =VLOOKUP(DATE(2009,10,5),H5:I7,2,0),...
  )

How to enter Texts in lookup_value

• Check spelling, for example "Martinez" instead of "Martines".
  You can avoid spelling errors by creating a validation list.
  
• Quote texts, for example =VLOOKUP("Susan",arguments).
  Excel interprets strings without quotes as named ranges.
  

How to enter Numbers in lookup_value

• Enter the number with all decimals, for example: =VLOOKUP(1.
  23,arguments) may return #N/A because the number in table_array is 1.
  225.
  Excel works with all the decimals behind the scenes.
  
• Don't quote numbers, for example =VLOOKUP("1.
  23",arguments).
  
• Don't use suffixes like: m for meters, " for inches, etc.
  Use custom cell format instead.
  
• Don't use prefixes like: $, etc.
  The $ in the index column must be a result of formatting.
  

If you apply above guidelines, you will surely get less or no unwanted errors due to a wrong lookup_value.
To be successful with VLOOKUP function you must dedicate time to prepare the backend list up to the point of being ready to be queried, after that, you must focus on entering the formula correctly.