Paypal Standard & Paypal Pro question

I recently upgraded to zen-cart 1.3.8a and, at the same time, changed from Paypal IPN - Website Payments Standard to Websites Payment Pro/Express Checkout combo. The "pay directly by credit card with Paypal" work just fine but when I try the Paypal option and confirm, instead of leading me to the Paypal website, I get the dreaded blank page.

My question is this: should I uninstall the Standard module completely to make the Pro module work, or does it make no difference? It is currently disabled but still installed.

I'm looking at all possibilities to solve the issue but an answer to that question would be a good start.

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... I get the dreaded blank page.
https://www.zen-cart.com/tutorials/index.php?article=82

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My question is this: should I uninstall the Standard module completely to make the Pro module work, or does it make no difference? It is currently disabled but still installed.
If you're using Express, you should uninstall Standard. It's always unwise to leave modules installed-but-disabled.

But, having Standard installed-but-disabled has no direct relationship to the blank-page problem you mentioned.

Thanks for the link but I know that page all too well already :P. The log files haven't been much use so far but I'll keep looking. I will try to uninstall Standard and see if anything changes.