Moss problem: Your change conflict with those made concurrently by ...

Question

I want to update some lookup field of a list when some feature is activated. To deal with this I made a SPFeatureReceiver for the feature. I debug my code and every thing was perfect until I do this:

sourceField.SchemaXml = sourceField.SchemaXml.Replace("List=\"\"", string.Format("List=\"{0}\"", targetGuid));

I dont understand why this happens because I am setting the AllowUnsafeUpdate to true.

The exception that I get is:

[Microsoft.SharePoint.SPException] = {"Save Conflict\n\nYour changes conflict with those made concurrently by another user. If you want your changes to be applied, click Back in your Web browser, refresh the page, and resubmit your changes."}

Please help me asap, thanks

Abel