When using VLOOKUP, you can only search one column and return a value from a column to the RIGHT of that column. Based on your formula, you're looking up the date in D10 in a table spanning A1:I6, so VLOOKUP is going to search column A for that date, and return the value from the second column.
Of course, this doesn't work because column A in your table doesn't contain dates. To lookup a value in one column and return a value from a column to the LEFT of it, use INDEX/MATCH, like so:
=INDEX($B$2:$B$6,MATCH(D10,$I$2:$I$6,0))
This searches I2:I6 for the value in D10, and if found will return the value from column B in the same row as the match. Change your ranges accordingly.