SSIS package fails on live release

Problem is I have an SSIS package that accesses Excel as its data source. This package is run by a C# .dll on an MVC website. The package works on all our test, UAT and staging servers fine but it fails on our live server.

• Access 2013 runtime is installed and the ODBC driver is in place. Permissions match on both.

• SQL Server 2014, Azure VMs for UAT, Staging and Live. Windows server 2012 on all.

• Access 2013 runtime is installed and the ODBC driver is in place. Permissions match on UAT and live servers on the temp folders and the folder that stores the uploaded .xlsx file. AceODBC driver is v15 and 32 bit. This is the same installation on all servers.

• Delay validation is true.

• Use 64 bit is false.

• All servers patched up to date.

I've pretty much exhausted the online things I can find. I must have missed something but I can't think what.

Errors are:

Initial Load Error: Excel Source failed the pre-execute phase and returned error code 0xC0202009.

Initial Load Error: SSIS Error Code DTS_E_OLEDBERROR. An OLE DB error has occurred. Error code: 0x80004005. An OLE DB record is available. Source: "Microsoft Access Database Engine" Hresult: 0x80004005 Description: "Unexpected error from external database driver (1)."

The event log just says:

A package failed to execute

Any help or suggestions greatly appreciated.

I have a little more info now.

The package works from the command line using dtexec.

It seems to be something to do with running it from the web site. T

he code itself is the same on both servers so it can't be that.

The app pools on both the servers that should be identical have the same user on them. It's a user that was set up by our Server dept rather than a built in one.

No extra configuation of permissions was required on the server that works.

Disk space is fine.

Adding permissions to various folders used by the process didn't work.