Hello all, I'm testing a workflow which uses my filter tool where one of the parameters is a tabular file, and a related parameter is a multi-column selector: Tool: http://toolshed.g2.bx.psu.edu/view/peterjc/seq_filter_by_id Snippet from tool XML, <param name="input_tabular" type="data" format="tabular" label="Tabular file containing sequence identifiers"/> <param name="columns" type="data_column" data_ref="input_tabular" multiple="True" numerical="False" label="Column(s) containing sequence identifiers" help="Multi-select list - hold the appropriate key while clicking to select multiple columns"> <validator type="no_options" message="Pick at least one column"/> </param> In most cases, the preceding tool will generate a tabular file with two columns - and the workflow has column 1 as the saved value. However, it is quite valid for the tabular file to actually be empty - in which case the number of columns is unknown and so the arguments can't be checked. Despite this, Galaxy attempts to check the column argument from the workflow and fails: Traceback (most recent call last): File "/mnt/galaxy/galaxy-central/lib/galaxy/jobs/runners/__init__.py", line 119, in prepare_job job_wrapper.prepare() File "/mnt/galaxy/galaxy-central/lib/galaxy/jobs/__init__.py", line 656, in prepare self.tool.handle_unvalidated_param_values( incoming, self.app ) File "/mnt/galaxy/galaxy-central/lib/galaxy/tools/__init__.py", line 2330, in handle_unvalidated_param_values self.handle_unvalidated_param_values_helper( self.inputs, input_values, app ) File "/mnt/galaxy/galaxy-central/lib/galaxy/tools/__init__.py", line 2369, in handle_unvalidated_param_values_helper raise LateValidationError( message ) LateValidationError Tool execution generated the following error message: Failed runtime validation of Column(s) containing sequence identifiers (An invalid option was selected, please verify) It seems to me this is a bug, and the late validation is being too strict where as in this case the number of columns is undefined. Peter