Redirected to "The page you requested cannot be found." page

I've been experiencing problem on my website (nutrientsuperstore.com) when adding a product to Admin->Catalog->Products->Insert->Product Name within Opencart v1.5.4.1 that results in always receiving a "The page you requested cannot be found" error. To date, I have been successful in adding all of my products (along with product names and descriptions) to Opencart, except for one: "Glucosamine Sulfate" (the name of a nutritional supplement).

Whenever I include those two words (and only those two words) within the Product Name and/or Product Description fields, I am returned a "The page you requested cannot be found." error. After receiving the error, I am still able to continue adding any other products. It only produces the error for "Glucosamine Sulfate."

Currently, I have intentionally misspelled that product's name in my cart and have now found that, by doing so, I AM able to add that product to Opencart. Could someone please advise what could be going wrong - Could this be a bug blocking my being able to add the words "Glucosamine Sulfate" to the Products section of Opencart v1.5.4.1? Thanks in advance.

Are SEO urls? Try adding the product, spelt correctly, but try a different SEO url to anything that you may have added in the past.

I also see that you have used an apostrophe (') in one of you glucosamine SEO urls. Perhaps this is causing problems. I think that the only punctuation you should use are hyphens or underscores (hyphens as spaces between words).

Are you being re-directed to a OpenCart 'page cannot be found page' ? If so, temporarily disable your .htaccess files which re-direct to said page. You may inadvertently be tripping a security system (ex. mod_security) with the post data being sent in (I have seen this happen before) that is configured on the server you are being hosted on.

anyhow disabling the htaccess should let you see the error being generated if you are seeing an OC page not found page.

Try to disable mod_security on your hosting (ask your admin). In my case, after clicking 'save' on product page, I was redirected to that "the page you requested bla bla...".
Disabling the mod_security solves the problem.