Learners’ difficulties in correctly using adverbs have long been reported in CSL/CFL research, and findings yielded in previous research have shed some lights on CSL/CFL learners’ patterns and causes of misuse. Many of the investigated adverbs in these studies, however, were subjectively selected by the researchers and might not cover the common errors in learners’ production. To more objectively identify common adverb-based errors in CSL/CFL learners’ writing, this study extracted adverb-based errors from the error-tagged Chinese Learner Written Corpus of National Taiwan Normal University and discovered that missing of adverbs occurred much more frequently than other adverb-based errors. Among the 2,923 tokens of omitted adverbs, missing of the adverb 都 dou ranked first, which accounted for 18% of the same error type. Further analysis of the 526 tokens of omitted 都 dou revealed that 都 dou was mostly misused when serving as a scope adverb (461 tokens). In addition, the omission of 都 dou often occurred when the quantified NPs included 每 mei, 所有的 suoyoude, 任何 renhe, 隨時 suishi, and 到處 daochu, taking up 56.62% (261 tokens) of the 461 tokens. A follow-up examination of how 都 dou is presented in the learners’ textbook indicated that the high percentage of omitting obligatory 都 dou in these sentences might relate to the inadequate explanation of 都 dou’s correct usage in the textbooks. Based on the findings, suggestions for future material writing are offered for CSL/CFL learners’ better acquisition of 都 dou.