After login in the backend, sometimes (not always) I've this error appearing in the dashboard screen.
It's very strange and I really don't know where to look. I tried to disable all plugins, clear the cache etc.. but nothing changes
In magento c.e 1.9, toCurrency() does not exiting at
Mage_Directory_Model_Currency class .That why create issue.
May be ,in your system there have custom code /or 3rd party extension which call this function using code like:
You need to remove this code from your system