Mistakes led to five police searches at properties linked to innocent people, the Interception of Communications Commissioner Sir Anthony May revealed.
His report said there were 17 serious errors in 2014 by public authorities or communications service providers.
Sir Anthony said errors could have a "devastating" impact.
The mistakes were made during activities to obtain communications data - the who, when and where but not the content of communications - under the Regulation of Investigatory Powers Act.
Overall, nine were caused by human error, with the remainder attributed to technical faults.
Errors in tracing information about internet activity led to the arrest of one person, even though they were unconnected to a child sex investigation, the report disclosed.
In one case, a public authority tried to trace the user of an email account used to groom a young girl as part of an investigation into child sexual exploitation, but missed out an underscore on the address.
It led to police searching the home of someone who was unconnected with the investigation.
The report also revealed that a revised code introduced in March that requires judges to sign off requests to access journalists' data had already been breached by two police forces, which were not named.
Sir Anthony said: "Any police action taken erroneously in such cases, such as the search of an individual's house who is unconnected with the investigation or a delayed welfare check on an individual whose life is believed to be at risk, can have a devastating impact on the individuals concerned."
The report said that in all instances where there were "very serious consequences", the people affected were aware of the error.
In the majority of cases, Sir Anthony said they were "incredibly understanding", while others have taken legal action.
State agencies were responsible for five of the errors and communications service providers were responsible for 11, with one blamed on an organisation referred to as "other party".
Sir Anthony declined to name the organisations responsible for the errors.
People were wrongly implicated in paedophile investigations because of botched attempts to access data, a communications watchdog has said.