Changing source links in powerpoint

I currently have a powerpoint with source links to other powerpoint slides.
These source links are currently internet address based links. I'm trying to
change these current internet addresses to new internet addresses and each
time I try I receive the error message: "You cannot use an internet address
here. Enter a path that points to a location on your computer or on the
network". I've been able to change the source links in the past and only
began to encounter this problem around mid December. Does anyone know how to
correct this or explain why I can no longer perform this function?
Thanks.
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klshaner