Help - Design format not printable on this product

Hello guys,

I am currently running into a problem on several products with the products being unavailable for me to choose and giving me the message: Design format not printable on this product.

Not sure what the problem is as the design works on multiple caps example but not the flexfit baseball cap etc. which i really wanted in the shop. I have tried the product wizard to import the items as well but without any luck.

Anyone had been having this issue and was able to solve it? Or any ideas to why the problem occurs?