You appear to be using MS Windows. I suspect you have Excel installed. xlsread() uses ActiveX connections to Excel to read data in the case of MS Windows with Excel installed. If you are using one of the last few releases, then xlsread caches connections to reduce overload instead of opening and closing the same file each time. That is probably causing problems for you.
In cases where you are reading the same file over and over again, you are probably better off using ActiveX directly. You can even create callbacks to get notified when the data changes.
In the meantime, try adding the option 'basic' to your xlsread() command; that will force it to read the file as a text file instead of using ActiveX to ask Excel for the data.
