Cisco Switching/Routing :: 4503-E Cannot Bring SFP Fiber Interfaces Up

I am trying to connect a 6509 switch to a 4503-E switch using single mode dark fiber over a distance of less than half a mile. Although a routine task, it does not work..We have a care 6509 switch where we concentrate all of our dark fiber connections for our remote sites. The 6509 switch already has 30 remote sites, most of them with 4503-E switches, connected in this way therefore it is a tested scenario. For the connections we use the GLC-LH-SM SFPs on both switches. Out of these 30 sites we had a similar problem with two of them, which we solved with the use of CWDM SFPs. With the CWDMs the fiber came up right away. However, I cannot keep using this solution because it is way too expensive! I had the losses of the fiber measured end-to-end and they are negligible (>0.5 dB).
 
In this latest case, like I said, we could not bring the connection up between the core 6509 switch and the 4503-E switch using the GLC-LH-SM SFPs. I then replaced the 4503-E switch with a 3560 and the link came up! Then I tried using a CWDM-SFP in the 4503-E, while keeping the GLC-LH-SM SFP in the 6509 and the link came alive again! Of course we already tried replacing the fiber patch cords with no luck. [code] I find it very weird for the link to work with the 3560 or with a CWDM in the 4503 but NOT with the SFP in the 4503!