Error in Management Reporter Data Mart performing initial integration

In the Data Mart log of a customer's MR Console, I'm getting the following:

[GL Transaction to Fact] has encountered an error. Processing will be aborted. Error text: One or more errors occurred.

I have edited the MRServiceHost.exe.config file such that it contains the following line:

<add name="Microsoft.Dynamics.Integration.TraceLog" value="4"/>

and restarted both MR Services to be sure, however no additional information is displayed in the Data Mart log - just the above error.

Any ideas?

For reference, this is MR 2012 RU4 integrated to Dynamics GP 2010 SP2, running on Windows Server 2003 x86.