Can't Encapsulate ISL in configuration for VLANs

I have a 3745 router (IOS = 12.2 (13)T that is not functioning and I have a 3725 (IOS = 12.2. (8)T5) which I am configuring to replace the 3745.  When I configure a VLAN on the interface the encapsulate command returns an invalid character error. I can only guess after many retries that the problem lies with the difference in the IOS versions since the encapsulation works with the 3745.  Any help would be appreciated.
stancrfcAsked:
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MrJemsonCommented:
Could you please cut and paste the exact command you are trying to implement and the error associated?
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packetguyCommented:
I don't believe the 3725 supports ISL. Cisco phased that out of its products years ago, due to the interaction problems I caused with the nonproprietary 802.1Q encapsulation.
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donmanrobbCommented:
I would just just dot1q as there isn't much difference. If you require all frames to be tagged you can use the vlan dot1q tag native command
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stancrfcAuthor Commented:
I found that I had the wrong feature set for ISL
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