500 error on second installation

I am attempting to install a second WP site on the same database as the first install. I’ve done this multiple times before on other servers with no problems.

I have tried installing to loan-review.biz/en/ on the lbwp database,
using the extension “uswp_”. Initial installation was successful, as
were past attempts… but after a short time everything fails and all I
get is a 500 error.

I emailed our host and have been giving the following error readout which, alas, means nothing to me:

Module RewriteModule
Notification SendResponse
Handler StaticFile
Error Code 0x800700b7
Config Error Cannot add duplicate collection entry of type 'rule' with unique key attribute 'name' set to 'wordpress'
Config File \\?\C:\Websites\Gould\loan-review.biz\en\web.config
Requested URL https://loan-review.biz:80/en/
Physical Path C:\Websites\Gould\loan-review.biz\en\
Logon Method Not yet determined
Logon User Not yet determined
 Config Source
    5:       <rules>
    6:                 <rule name="wordpress" patternSyntax="Wildcard">
    7:                     <match url="*"/>

I gather that A) something is undefined and B) there is a duplication somewhere.

Our host has been pretty unhelpful, so I’m hoping you all can help with a solution. ??