> bsf portc,scl
> bsf portc,sda
> goto $+1
> bcf portc,scl
> bcf portc,sda
> goto $-5

More than likely a read-modify-write issue

http://www.piclist.com/techref/readmodwrite.htm

As Bob suggests, separate the port bit instructions

Here's an illustrated example of how a h/w problem can be caused
by s/w that is too fast (especially on the PIC-like Scenix)

http://www.sxlist.com/techref/scenix/sxrmw.htm
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