After installing web calender from fantastico, you will get the following error.

Cache error: Could not write file /tmp/d16090f5de830d7675276b6523ce3f59.dat.

Solution :

Edit settings.php file which you will find under includes folder.

Search for
db_cachedir: /tmp
and replace it with following
db_cachedir: /home/user/public_html/tmp

Save the file then create tmp folder under public_html and assign 777 permission.

That is all