Error message data: E_ERROR:1 0: Illegal offset type in file product.php model

[Kuubs]

I get an error from Virtuemart productdetails page:

/index.php?option=com_virtuemart&view=productdetails&task=recalculate&format=json&nosef=1&lang=nl-NL

This comes from accessing my product page.

Error message data:
E_ERROR:1 0: Illegal offset type in file: /administrator/components/com_virtuemart/models/product.php line: 1172

If I check the line it has something to do with the cache. The cache gives a lot of issues anyway, so if I can disable it ouright would be great

self::$_cacheOpt[$virtuemart_product_id] = $opt;