With a maint plan when you check reorganize data and indexes for optimization the update stats box greys out.  You will need to create another maint plan to run update statustics.

sp_spaceused

sp_helpdb

What was the error encountered when the inserts failed?

Does the application use stored procedures or in line SQL?

I would also incluse in your maintenance to run sp_recompile on all user tables, which will force all associated procedures...

You can thow out the idea of a disk problem:

avg disk queue .568

What is the OS and MS SQL Server version you are running? What utility are you using to do the backups? Is the application using stored procedures or in-line SQL? 

Can...

I like to insure basic maintenanace takes place before I look at the applications.  Do you have a nightly/weekly/monthly window that you can introduce maintenenace to the MS SQL Server? The...

Create a temp table with and identity column and the email adress select the data into the table and then use Ray M's approach.

This may not work if the data...

You can use SQL Profiler, sp_who, sp_who2, and sp_lock to monitor this activity.

Locking is a normal activity within a database and is used to maintain consistency and integrety of...

Can you log into the server and get to the db through EM with user in that group? Is the db in 'single user' or 'dbo use only' mode?

Post the SQL and Procedure.

Does this group exists as a user in the default database? If it doesn't add it. If it does, is the database user name the same as the login name?

db...

If both those jobs above are it you may not be doing the proper maintenance to support this application.

Basic maintenenace example:

Full database backup: Daily (Recovery to point in tiime within...

Are you doing maintenanace? How often?

The box is not CPU or I/O bound. My first question before looking at the application would be what type of maintenenace is being performed outside of backups. (DBCC's, indexes rebuilds,...