Umbraco Version 4.7.2
CMSImporter PRO Version 2.2.1
DateFolders Package Version 1.4

Computer 1
Windows 7 (64 Bit)
Service pack 1
3 GB Memory
80 GB free hard disk space
IIS Version 6.1 (Build 7601 Service pack 1)
ASP.NET Version 4.0

Computer 2
Windows Server 2008 R2 Enterprise (64 bit)
Service pack 1
4 GB Memory
141 GB Free hard disk space
IIS Version 6.1 (Build 7601 Service pack 1)
ASP.NET Version 4.0

I am importing archive web pages to Umbraco using CMSImporter and the DateFolder package to sort them into dated folders as they are imported.
Currently I have over 31,000 pages imported into Umbraco.
I began to run into an issue at about 25,000 pages where the folder I was importing into would lose all its sub folders on the Umbraco backend.
Checking the database the data still existed and was not flagged as deleted so it should have been visible, there was also no log entry indicating a delete had operation had occurred in Umbraco.
Restoring the database to an earlier version would restore the folders.
At times the folders would be visible and accessible directly after the import then disappear when restarting the server or reloading the website from the browser.

This occurs when importing on both of the computers above but strangely it seems less severe on computer 1

Using Importing and restoring of the database when there was issues, I got to 31,000 pages imported but now instead of just the import folder vanishing the entire backend folder structure vanishes, all that is displayed is the content folder.
The backend attempts to load the content sub folders for about 30 seconds then displays nothing

This happens on both computers displayed above, although initially I was able to restore the DB on computer 1 (the slower one) and the folder structure would display then by backing the DB up and putting it back on the server the folders would display again on the server, but now I’ve reach a point where the entire folder structure wont display either machine.

The folder structure that was being created looks like the following:

Archive folder
- Sub folder
- 2012
- 03
- 01
- 02
- 03
Etc....

I have about around year of dates imported, spread over the 2009 - 2012 period and around 300 pages per day imported

Is there an Upper limit to the amount of pages or folders Umbraco can display?
I am veering towards not having enough memory but the problem is the machine with only 3GB had less problems displaying the folders than the one with 4GB and there are issues to get more assigned.

Any ideas?