Unable to read before writing

[nanakawa777]

Version is 1.0.0b4
Example:

*** Settings ***
Library  ExcelRobot
*** Variable ***
${xls}    ${CURDIR}${/}testxls.xls
*** Test Cases ***
Read
    OPEN EXCEL  ${xls}
    ${data}  READ CELL DATA  Sheet1  0  0
Write
    OPEN EXCEL TO WRITE  ${xls}
    WRITE TO CELL  Sheet1  1  1  Test
    SAVE EXCEL

After running, the Read passes without a problem, while the Write reports errors that the file is being used.