plm package: variable lengths differ

Hi R users:
I am conducting high frequency data analysis based on plm package. It works fine for the dataset with lower data frequency but not for 1-min dataset. Listed below is the error message:pooltest(form, ?data ?= ?E, ?effect ?= ?"individual", ?model ?= ?"within")Error in model.frame.default(terms(formula, lhs = lhs, rhs = rhs, data = data), ?:? variable lengths differ (found for 'lag(IOB, k = 1)')Calls: pooltest ... model.frame.Formula -> model.frame -> model.frame.defaultExecution halted
I have encountered the same error message when I tried the other functions for testing and estimation in package plm. I check the original dataset and all the columns are of the same length but the error message indicates otherwise:?variable lengths differ (found for 'lag(IOB, k = 1)').?lag(IOB, k = 1) denotes the lagged term of variable IOB with one period.?
I googled and found some people raised the similar question but no helpful tip is provided yet. For example,?R help - length of variable in mlogit

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 ?Could some people share advice and help in this regard?
Best regards,
Weihan