Error executing Query - An exception that could not be caught occurred.

When executing a query from BEx, I'm getting an ABAP dump

UNCAUGHT_EXCEPTION

An exception assigned to the class 'CX_RSR_X_MESSAGE' occurred in a conversion exit or another procedure, which was called internally.

Since this exception was not caught within this procedure, processing was terminated.

We are in BW3.5 SP11.

Any ideas/fixes?