RuntimeError: Can't begin a new transaction

This error occurs when you try to begin a new transaction without first committing or rolling back the previous transaction. In other words, you cannot have multiple transactions running concurrently on the same connection.

To fix this error, you need to either commit or roll back the previous transaction before beginning a new one. You can do this by calling the `commit()` or `rollback()` method on your database connection object.

For example, if you are using Python's `sqlite3` module to interact with an SQLite database, you can do the following:

import sqlite3

conn = sqlite3.connect('example.db')

# Begin a transaction
conn.execute('BEGIN TRANSACTION')

# Do some database operations...

# Commit the transaction
conn.commit()

# Begin a new transaction
conn.execute('BEGIN TRANSACTION')

# Do some more database operations...

# Commit the second transaction
conn.commit()

# Close the database connection
conn.close()

Make sure to always properly handle transactions in your code to avoid this error and ensure data consistency.