An MS created by the EVLA archive which uses CASA 3.2 (after 18 May 2011) will be incompatible with certain tasks in CASA 3.1. For example, the task 'split' will produce errors such as the following:

MSTableImpl::addColumnToDesc - Invalid data type: 26,
2011-07-14 13:21:42 WARN split::SubMS::addOptionalColumns() Could not add column PhaseDir_Ref to /data/perseus2/casa_data/n7016/3c48_spw0.ms/FIELD
MSTableImpl::addColumnToDesc - Invalid data type: 26,
2011-07-14 13:21:42 WARN split::SubMS::addOptionalColumns() Could not add column DelayDir_Ref to /data/perseus2/casa_data/n7016/3c48_spw0.ms/FIELD
MSTableImpl::addColumnToDesc - Invalid data type: 26,
2011-07-14 13:21:42 WARN split::SubMS::addOptionalColumns() Could not add column RefDir_Ref to /data/perseus2/casa_data/n7016/3c48_spw0.ms/FIELD
2011-07-14 13:21:42 SEVERE split::ms::split Exception Reported: RecordInterface: field Ref is unknown

The preferred solution to this issue is to install CASA 3.2.1, which is available at http://casa.nrao.edu/current_casa.shtml. Alternatively, one may download the SDM file set from the EVLA archive and fill the MS using importevla in CASA 3.1.