<p>After installing asp.net (and aspnet_regIIS.exe -i) the site doesn't accept my default.aspx page. When trying to access it I get a 404.
When hitting directly to my mvc pages (/search.mvc for example) it works like a charm.</p>

<p>We checked the website configuration and noted that there are no .aspx references in the scriptmaps node.</p>

<p>What am I missing?</p>

Probably you are missing the .aspx references in the scriptmaps. SCNR. ;-)
More seriously, are they there at the "Web Sites" properties level in IIS manager? What is the output you get when running
```
aspnet_regIIS.exe -i
```
?
Mine says:
```
C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727>aspnet_regiis.exe -i
Start installing ASP.NET (2.0.50727).
..............................
Finished installing ASP.NET (2.0.50727).

C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727>
```