Im trying to insert some Opportunities, but i get this error:
System.DmlException: Insert failed. First exception on row 0; first error: CANNOT_EXECUTE_FLOW_TRIGGER, The record couldn’t be saved because it failed to trigger a flow. A flow trigger failed to execute the flow with version ID xxxxxxxx. Contact your administrator for help.: 
Im working on sandbox and this trigger comes from managed package, so i cant just deactivate it.
You have two options
1.Uninstall the application that's causing this .To do this it's important to note business impact of removing the package .Keep this as last option.
2.Go back to the publisher or owner of the application and ask them to fix this issue. The publisher can debug or figure root cause via their LMA or ISVForce .
Prefer this over first but if option 1 has no impact just ask users to stop logging and you can do data load and restore back the package once you are done with load .