I have an apex trigger that runs when a Chatter message is posted. I also have a custom object.  I would like to write text to the custom object from my apex trigger.  Everything works fine when an admin user posts a chatter.  However, when a non admin user posts a chatter I get an exception:

Apex trigger company.test caused an unexpected exception, contact your administrator: company.test: execution of BeforeUpdate

caused by: System.DmlException: Insert failed. First exception on row 0; first error: OP_WITH_INVALID_USER_TYPE_EXCEPTION, Operation not valid for this user type: []: (company)

How do I get this to work for non admin users?

Curious to know if we can use the dataloader to import a chatter attachment?

1. We 1st import 1000 contacts

2. We then use the salesforce id and upload the associated document to a chatter message.

We do it with regular attachments but need to use Chatter for this use case.

Thanks