The Express VIs support only numeric channels, and some time stamp channels. The error you're seeing typically comes from files that contain string channels. You can double-check that by using the TDMS File Viewer from the TDM Streaming palette. The functions on the TDM Streaming palette (e.g TDMS Read) allow for easy access to particular channels, so you wouldn't have any issues with unsupported data types. You can check the "Write/Read Event Data" example VIs for more details on how to handle numeric and string channels in the same file.
Hope that helps,
Herbert
