Hi,
I truly understand the problem. Unfortunately i don't have the solution. Weirdly, it happens in some website rarely. It is not due to JAVA conflict though, it is because of something that i have never figured out. It happened to one of our clients before and i have spent hours in his server, without finding actually what causes that.
Are you using Virtuemart 2.0.12b+ and Virtuemart AIO 2.0.12b+ ? Please make sure you are using the latest versions. At least use the AIO 2.0.12b, because the pricing calculations and things like these are held by this component.
If you already have the latest version; the best thing i can offer you is to disable the "plus and minus" sign completely
And add this LINE:
<input type="hidden" class="quantity-input js-recalculate" name="quantity[]" value="1">
Which will let you add "1" product right away once the add to cart button is clicked.
OR put a manual dropdown box there. Up to 9 quantity or whatever quantity you want. Which will be something like this:
<select class="quantity-input js-recalculate" name="quantity[]">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
<option value="6">6</option>
<option value="7">7</option>
<option value="8">8</option>
<option value="9">9</option>
</select>
OR you can use the regular input text field what user can change the value simply by editing it. It will be something like:
<input type="text" class="quantity-input js-recalculate" name="quantity[]" value="1" />
Cheers.
Flexible Support Team.