Simple Excel Question: VLookup Error
This is a common result of imprecise matching, such as with whitespace problems. 

For example, if you imagine that the grey shading used in codeblocks on StackExchange represents the whitespaces in your Excel cells, then 
  AK 
is technically the same as 

AK  


You can trim and/or use wildcard chars to allow matching to skip spaces. For example:

=VLOOKUP(CONCATENATE("*",TRIM(A2),"*"), $E$2:$F$5, 2,FALSE)