is it possible to create another .aspx page in DNN?

I realise the pages are made up on the fly from which ever modules are selected etc.

I've seen the default.aspx page and wondered if I could place my own custom page here too?

As a test, i copied and pasted default.aspx page and renamed it to default2.aspx and renamed .vb page etc too, but even this creates an error.

Is it a permissions issue or is there some other code somewhere which only allows "default.aspx" page to work and strictly no other?

thanks,

we are basically trying to insert our own page which has some formulas on, and then returns a specific form (depending upon the users input),

the form then writes the users entry from the form into a database table.
 

we have the above working ok in its own page eleswhere, so we could just use an iframe to this, but thought it may be best if our page is in the same place as our DNN content.

I would suggest that you use the IFrame approach for now then convert your custom page to a DNN module which will then be able to make use of the DNN framework capabilities for skinning, localization, and user authentication/authorization, etc.