Returning preg_match() error, incorrect trigger function

[marvel]

Hello,

When I try to create a trigger with this expression:
{myhostname:vfs.fs.size[c:,free].last(0)}<1500000000

it gives the following errors:
preg_match(): Compilation failed: unknown option bit(s) set at offset 0 [api/classes/CTriggerExpression.php:93]...