Too Much Memory Usage

Good day to all,

I'm new here, so I don't know if this is the right forum to post my problem. I
have a web application written using C# .net 2005 (W/ajax). The application has
a module that uploads data from excel file to the sql server 2005 database. w/c
is by the way, i'm using SQL 2005 Express Edition, the app can upload up to more
than 10,000 records from an excel file. Everything is ok until it was deployed
in a test environment, while having a run through with the system, the
application encounter an error after which, we cannot log in to the system
anymore. I restarted the server (web and sql server in 1 machine running winxp)
then I can log-in again in the system. When I'm tracing where the problem came
from, I noticed that the memory usage of sqlservr.exe increases everytime the
app connects to the server. I already fix some code to close some objects that
might have caused the high memory usage, then I run sp_who in the management
studio and there are still connections used by the app AWAITING COMMAND. Then I
manually kill (using kill spid) connection that are left opened by the
application. But the mem usage of sqlservr did no decrease. Is there a way to
release the memory usage of sqlservr.exe? In ASP.Net ? I have a hint that this
has been causing the error. Thanks a lot.