The FTPExposer activity contains a restriction of 64 characters for the name of the incoming TIFF files. When the TIFF's file name contains more than 64 characters, you get the above messages in the FTPExposer.log file. This restriction exists in all versions of Nexus.
You need to check the output name settings in your Rasterize Separations or Assemble Separations activity.
It consists of several parts. It typically includes the Nexus Job Number, the input file name and the separation name. If any of the TIFF files has a name which consists of more than 64 characters (including the file extension .TIF), then you need to reduce the name of the TIFF file.
You can do this either by changing the name of the input file, by changing a long separation name to a shorter value or by changing the settings in the Rasterize Separations or Assemble Separations activity.
Keep in mind that separation names can have a variable amount of characters, so you need to check the name of the output TIFF file for the separation with the longest name.