Hello Masumi Osawa ,
It is always advisable to post the full error stack as this will provide us with useful information.
First please run a verification (F8) on the file, this should show you which segment(s) are causing the error.
This is likely due to a missing/deleted tag during the merging of segments and may require you to create a new project, then pretranslate through your TM- without merging segments.
Lydia Simplicio | RWS Group
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