When using the code example from Adobe for cfcalendar we have seen customers experience 404 errors within the frame containing the flash form. On these occasions it was caused by a Re-write rule within their .htaccess file. If allowing specific directories then denying the rest as in the code example below:

Code:
RewriteRule ^(flex2gateway|flashservices|cfide|CFFileServlet) - [L,NC]
RewriteRule ^(.*)$ /missing.htm?path=$1
These rules allow for the flex2gateway, flashservices, cfide, CFFileServlet to be served without checking any other rules. For the cfcalendar tag to work you will also need to add "CFFormGateway" to the list of excluded folders. Other solutions have also been to make sure the "check if the file exists" is unchecked in IIS within the ColdFusion wildcard mapping.

The working example:

Code:
RewriteRule ^(flex2gateway|flashservices|cfide|CFFileServlet|CFFormGateway) - [L,NC]
RewriteRule ^(.*)$ /missing.htm?path=$1