I believe the security is at a table level, so for example any data in the master inventory file tables tInvent, tInvbyLn, tInvPrc, etc. is accessible to an ID that has access to inventory.

When the invoice is being imported, it may be going wrong where the import file specifies the G/L accounts, which are already linked to the inventory items. 

It may be different when using the SDK and the .NET methods, I would think it should work the same as when importing from a text file - the program should be capable of processing an imported sales transaction of all defined inventory & service items, without being passed the G/L accounts. 

That error message when importing from a .IMP file would be because the import module is interpreting the imported G/L account data on a line as being an over-ride of the default account, and the user has access to process an invoice, but not to choose the G/L account.

I hope that helps, please post back.

I think i found the issue, i had to provide the user with third party access.

however, when the user is logged into the app to import, it seems that he can not stay logged in to simply?

is there any work around for this?

so both can be logged in?

the importer program reads/writes to the database.

Yes, sorry I didn't read your original post carefully, all access to the data outside of the Sage 50 program requires 'third-party access' be enabled.  

If the import utility is opening the database in multi-user mode, then a work-around to stay logged in while running the import, is to create another ID that is only used by the import program.  

If your import utility is hitting a lot of inventory items and there are conflicts, problems such as slow performace could arise from that.

I'm not sure if the restriction on one login per ID on a workstation is a license restriction (one login per user ID), or a technical one (one TCP/IP address + Port per user name).

Multiple logins using multiple User IDs, from a single workstation, will work.  I use that to run reports from one workstation in Access or LibreOffice while Sage 50 is running.

We have ran out of licenses to use for just the importing processes, so that could be a problem and if possible don't want to purchase another one.

It just seems too much work to log off simply accounting to import and then login, since simply is always running on our machines and import orders come in randomly during the day.

From a technical standpoint, you may be able to use the SYSADMIN license for importing data.  

Whether or not that will work in your situation, I can't say.