Odoo Troubleshooting and Security Enhancement

General information for the business: We sell cleaning products
Kind of development: Customization of existing program
Platform: OpenERP
Description of requirements/functionality: I'm looking for someone very familiar with the Odoo POS and setting it up and configuring it correctly. First, I'd like to address two new issues I'm experiencing. My Odoo POS was working properly previously, but now it is disconnecting from the internet when I try to print an invoice. It then throws a syntax error saying unexpected end of file. I think there must be a problem with the data as there is no internet problem. Every once a while, I can get an invoice report to print correctly from the POS, but I haven't been able to identify the problem yet. I need this fixed.

Secondly, when I go to close a journal entry, I get an error (shown below). It might have something to do with the fact that I had multi currency checked in the configurations and then I deselected it and now it throws an error when I try to post the closing POS journal entry. Other Odoo users have experienced this, e.g., on the following link: https://www.odoo.com/forum/help-1/question/im-trying-to-post-a-journal-entry-in-a-not-multicurrency-company-and-im-getting-the-error-below-any-idea-hot-can-i-fix-it-66757

ValidateError
Field(s) `currency_id` failed against a constraint: The selected account of your Journal Entry forces to provide a secondary currency. You should remove the secondary currency on the account or select a multi-currency view on the journal.

DESCRIPTION OF ENHANCEMENT:
1.) I would like to update security privileges such that the Product Cost Price field and Supplier Information are only viewable by users who are Administrators or Purchase Managers. Right now, all sales users see this info and it shouldn't be the case in our company.
Specific technologies required: Odoo
OS requirements: Linux
Extra notes: Possibility of continued work as we have more enhancements going forward.