Some software like Microsoft IIS (4,5) update their log file using a special cache technic.
Here is how works Microsoft IIS :
On the first HTTP call IIS writes a 64Kb block of spaces in the log file with the first log row.
On the second HTTP call ISS just updates the 64 block of spaces with the new information. In that case fLogViewer cannot detect an update because the file size or date did not change. The Windows notification does not work either.
When the 64Kb block is full IIS create a new one.

fLogView 3.8 is now able to detect this kind of change. See the Options dialog