Acrobat Pro will not open additional pdf files !

 The new version of the interface is terrible and I have disabled this. I did so believing it would also fix the other problems, one of which is the inability to open new pdf files! The error messages say "a running instance of acrobat has caused an error". I can restart acrobat and open one pdf but it will not open a second document. The error message does not appear straight away either but suddenly appears in multiple copies after trying several times to open a new pdf. I am paying for software which is meant to be able to manage multiple pdf documents. What is going on?! If this is not fixed soon I will be cancelling this subscrition and will be looking for alternative sofware.