Web server: IIS6 will not serve classic ASP pages

I have a problem where one of our servers will not serve classic ASP pages.
When I navigate to the url, say http://example.site/folder/default.asp I will receive the following message

the connection was restarted
The connection to the server was restored while the page was loading.

- The site could be temporarily unavailable or very busy. Try again in a moment.
- If you can not load a page, check the network connection of your computer.
- If your computer or network is protected by a security server or proxy,
Make sure that Firefox has permission to access the Web.

However, if I browse to http://example.site/folder/default.htm, the page is served correctly.

I have also noticed in the HTTPERR log file a large number of Abandoned Connection entries.

2019-05-15 16:12:17 xxx.xxx.xxx.xxx 1156 xxx.xxx.xxx.xxx 80 HTTP / 1.1 GET /folder/TestFile.asp - 998577302 Connection_Dropped DefaultAppPool

This page is running in a Windows Server 2003 box running IIS 6. I have verified that the Active Server Pages web service extension is allowed, that asp is registered as a MIME type on the server, and that the Windows Active component is registered. Pages is installed.