you need to request the properties of the mime field type and there are multiple mime fields so you need to use the plural mime fields
(value of it, name of it) of mime fields of bes fixlet whose (name of it = "BES Clients using Main BES Server instead of BES Relay - Manual Selection (Primary BES Relay Not Set)")
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( Mon, 12 Apr 2004 23:42:34 +0000 ), x-fixlet-first-propagation
BES Warn Important, x-fixlet-domain_attributes
The error is saying that the mime field does not have a default return value that is a string - more about that in this post: