For some calculations the original source texts need to be available. For example, for Concord to show you more context than has been saved for each line, it'll need to re-read the source text. For KeyWords to calculate a dispersion plot, it needs to look at the source text to find out which KWs came near each other and compute positions of each KW in the text and KW links.
If you have moved or deleted the source file(s) in the meantime, this won't be possible.
If the files are networked ones, WordSmith by default will show them greyed. To detect whether each text file is still available across the network can slow things down. If you do want to have whether files are still present checked, see Advanced settings | Advanced | Plots, Prompts.