The error message indicates that the 'data' variable passed to the 'pearson_fusion' function is still a numpy array, even after converting it to a pandas dataframe. This could be because the 'data_array' variable passed to the 'minimize' function is still a numpy array.
To fix this error, you need to pass the converted pandas dataframe to the 'minimize' function instead of the original numpy array. You can modify the code as follows:
```python
import pandas as pd
# Convert data_array to a pandas dataframe
data = pd.DataFrame(data_array)
# Pass the pandas dataframe to the minimize function
res = minimize(objective_function, [0.1]*6 + [1000], args=(data,), method='Nelder-Mead')
```
This should ensure that the 'data' variable passed to the 'pearson_fusion' function is a pandas dataframe and the 'corrwith' method can be called on it without errors.