problem when installing themes

I have tried to install 4 different themes and each one is giving me this error:
Warning: fopen(/home/mothmee1/public_html/wp-content/themes/cosmode/style.css) [function.fopen]: failed to open stream: No such file or directory in /home/mothmee1/public_html/wp-includes/functions.php on line 3598

Warning: fread(): supplied argument is not a valid stream resource in /home/mothmee1/public_html/wp-includes/functions.php on line 3601

Warning: fclose(): supplied argument is not a valid stream resource in /home/mothmee1/public_html/wp-includes/functions.php on line 3604

I have contacted my hosting provider and asked them to make sure the fopen() PHP function is enabled, which they have done.

I then deleted and re-uploaded one of the themes and it still gave me this error message.

the stylesheet is there, the header appears to be fine – what else could be causing this?